Mid LiFePO4 Cruisers?

[SoSound]

I have been following the H49/50 Battery replacement thread, with increasing interest. As I read through the posts and search for prices and information on each of the components of a new battery system, I am starting to think that it might be people like me, with a medium to small sized cruiser, who would get the biggest bang for our buck by upgrading our batteries to modern technology. Also borrowing from another recent thread on the Benefits / drawbacks of going bigger, I would like to ask for feedback on the benefits vs. costs of upgrading the existing FLA batteries in our 34 foot cruiser.

I would like to ask for clarification on a few things, and focus on the components and details required to figure out what it would take for me to replace my existing (19th century technology) FLA batteries with a 21st century upgrade.

In our current cruising lifestyle, the only thing that we would do but cannot do while at anchor, is use our small (700W) microwave to heat water and coffee, or an electric kettle to boil water. We have no problems staying away from shore power or running our engine to recharge during the summer months, but during spring or fall I find that I need to raise the ends of my flexible bimini mounted solar panels to improve charging. If we encounter several consecutive cloudy days and really cool nights, then we start getting nervous about our available battery power, as the solar charging struggles to keep up with the demands of longer evening use of interior lighting, and the power consumption of both the refigerator and forced air heater.

Another goal of this upgrade would be to move our house batteries to different location. I have two G31 batteris are stuffed into the front of my engine compartment right up against both the motor and the companionway steps. The start battery is located below a covered seat in the aft berth. The owners manual actually shows the house battery in the aft berth, but I don't think there is enough space below the top of the compartment to fit FLA batteries with their boxes and tops. If there is enough space available, I'd like to swap the two banks and put the start battery in the engine compartment and the new house batteries near the battery chargers, controllers, and switches in the aft compartment.

As may be the case with many of us, my system is a bit of a mix of original equipment and piece meal upgrades, enhancements, and replacement components. Our current battery and charging system consists of;

• Batteries; 2 G31 FLA 105 Ah (house), 1 G24 FLA (start)
• Sterling Pro Charge Ultra PCU1230
• Alternator - Valeo 120A (not externally regulated)
• Cristec MOSfet isolator RCE-150-1E-2IG
• 220 W flexible solar w/ Victron MPPT 100/30

 

[dlochner]

As with most upgrades on boats the first issue is the intended use. The other factor to consider is the cost of upgrading.

Looking at your system, you have a lot to upgrade before LFP batteries to take advantage of the upgrade.

The biggest advantage to LFP is rapid recharge, i.e., the ability to accept a lot of current throughout the charge cycle unlike LA batteries. The alternator is probably not suitable for LFP batteries as the batteries will drive the alternator output to levels it wasn't designed to reach. This will cause it to over heat and burn out the electronics in the alternator. If your charger has a LFP setting or if you can customize the settings, then it will be suitable to charge the battery, but offer little speed advantage over LA batteries.

The second big advantage is more usable capacity. LA batteries should only be discharged to 50% SOC, LFP can be discharged to 00% SOC with minimal damage, however it is better to limit to about 20% SOC. This yields greater usable current in a similar sized package. In your case you would go from having ~100ah of usable current to about ~150 ah. That's a 50% increase with a 50% decrease in weight.

The other advantages, lighter weight, more charge/discharge cycles, less maintenance are nice benefits, but probably shouldn't be the main reasons for upgrading.

With planning, it is possible and reasonable to execute the upgrade over several seasons to spread the costs out. Initial costs will include a new Class T fuse, a DC-DC charger, some new cabling and perhaps switches. To take full advantage of all of LFPs benefits, add a new higher capacity charger and a larger externally regulated alternator. A good battery monitoring system should be in all DC systems, and especially in LFP systems.

We transitioned to LFP from 4 GC batteries over several years. The first step was adding Firefly Batteries and a new high output alternator and monitoring system and 300 watts of solar. This upgrade was essential for our plans to spend a year cruising the East Coast and Bahamas. It served us well. With the recent price drop in LFP it was a simple decision to replace the FFs, which have proven to be unreliable. Making the the change gave us a 50% gain in total capacity and 150% of the usable capacity of the FFs.

Your mileage, of course will vary.

LFPs are clearly the new darling of the cruising set and for good reason. Whether it makes sense for you depends on how you plan to use your boat and your energy consumption. Retro fitting LFPs is not the right path everyone.

 

[Hayden Watson]

Much of what you currently have is acceptable for use in an LFP house/ FLA start systems.

The biggest thing for that setup is to fully isolate the start and house banks for all loads. The FET based isolator makes a connection from the alternator to each of the batteries. For alternator charging, 14.2v is good for boat batteries so they will play nice together with the separation by the isolator. The one challenge I have come across with this system is that if I go several days of short runs under power it is possible for the start battery to not get a full recharge because the LFP is keeping the voltage down in the 13.2v range which means that the FLA is also only getting to 13.2v. To overcome this, I turn off the charging to the LFP for 15-minutes in the App to top off the FLA. Doing this I have not had any problems in the past two seasons with my 14-year-old AGM start battery.

Your alternator is not the best for rapid charging of the LFP because as Dave said, it will cook itself if you do not have a way to current limit it or at least let it have some time off to cool. There are two ways to resolve this. Add thermostatic control to the internally regulated alternator. Here is a video on that process.
Another option is to remove the internal regulator and change it to external regulator. That can be done by taking your alternator to any alternator shop and then can do the conversion. If you go that way, the Wakespeed WS500 is the top of the line for features that support LFP. I am not a fan of the DC-2-DC route because it typically provides much less power to the LFP and can still let the alternator get too hot especially if you are running at low speed because it is not monitoring the temp.

Your solar setup should be fine as is with some programing change.

 

[Hayden Watson]

I will say that going from a 210Ah Lifeline 4D to a 560Ah LFP was life changing as far as our cruising goes. We used to need to either motor or run the generator 2-3 hours each day to keep up with our power needs. Too many power-hungry uses as in heat, fridge and the surprisingly big one two laptop computers. We now can go 3-4 days without charging and most of the time, we can recharge durning a motor from one island to the next. I did have one day when I was down to about 60Ah and we fully charge motoring from Eagle Harbor to Sucia but I cheeted. I was motoring and also had my Honda generator runing in the inflatable so was putting in about 120A. I am in the planning stage of building a new alternator that will be able to charge up to 200A but have the ability to throttle it down to 80A or so if I need to motor at max speed.

 

[Johann]

I would say with the shore charger you’re fine. Unless you are powering it through a genset and trying to minimize runtime, anything close to 0.1C (after subtracting DC loads) is adequate since that would get you fully charged at a dock overnight.

 

[dlochner]

As the saying goes, there are many ways to skin a cat or build a LFP system. There is no best way, however there are some wrong ways.

Once we begin to move away for the old FLA battery systems and towards AGM and LFP old practices begin to not work. In general practice, the start/reserve battery continues to be a LA battery. As @Hayden Watson points out, the charging profiles for LFP and LA are different and it is easy to build a system that under charges the LA battery or over charges the LFP, both bad. Hayden has opted for a manual way of ensuring the start/reserve battery is frequently charged. I'm much too absent minded to rely on a manual system, however, I do want the ability to override any automatic system.

Away from shore power, the big question is how to safely and efficiently charge the LFP battery. And the bigger the LFP bank, the more challenging it becomes. Off the grid charging sources boil down to 2 options, a massive solar array or the alternator. Some rough back of the envelop calculations suggest a 600 watt solar array would be needed to put 150 ah back into a LFP battery. Set this aside for now.

Charging the LFP bank directly from the alternator is more efficient than charging the start battery and then using a DC-DC charger to charge the the LFP. However there are a couple of downsides to charging the LFP directly from the alternator, a BMS (Battery Management System) dump and heat. A BMS Dump occurs when the BMS shuts down the battery while the alternator is running, this causes a huge voltage spike which fries the electronics in the alternator. There is a simple and a complex work around for this problem. As mentioned earlier heat build up is a problem not as easily solved.

While the Valeo 120a seems like it could produce enough current, that rating is likely a cold rating, in practice the alternator will probably run hot even with an external regulator and its output will be much lower on average. In other words, the alternator is not designed to produce 120 a for an extended period of time. Alternators designed and built for extended high out put, like the Balmar XT alts, are built to produce more amps at low rpms than most stock alternators. They also have more efficient cooling systems including dual fans. The thinking behind this approach is to get more power production out of normal cruising operations and reducing engine run time.

So, for alternator output the question is send it to the start/reserve bank or directly to the LFP bank? If sent to the LA start/reserve bank, the alternator is well protected and the start bank is always charged at the expense of rapid charging of the LFP bank. If sent to the LFP bank first, then the alternator needs protecting and a way of charging the start/reserve bank is necessary, for the benefit of rapid charging of the LFP bank and reduced engine run time for charging.

All this brings me back to the question I raised early, how do plan to use the boat and what is your power consumption? A few questions to ask yourself:

What is the average daily power consumption while at anchor?
What is the average daily power consumption while sailing?
How long do you want to go without any charging?
How fast do you want to recharge the battery from a deep discharge?

The answers to those questions will set the parameters for the storage, use, and charging systems on your boat. What works for me, or for Hayden, may not be the best system for you.

 

[dLj]

I feel going to LFP batteries is a major change in systems. One thing no one has mentioned is they will take full current right up to being full, then they shut down taking current. It's almost like a switch being turned off in you alternators. You should put in protection to avoid blowing your diodes. I'm not sure you can do that without going to external regulation.

I did this upgrade in my boat, but I'm living on it. For me it was a no brainier as I had to replace all my batteries anyway. Very glad I made the switch, but your use is not the same as mine.

dj

 

[Hayden Watson]

I loaded the wrong video on adding the thermal switch to an internally regulated alternator. I uploaded the "What" needs to be done not the "How" to do it. Here is part two.

 

[Hayden Watson]

I feel going to LFP batteries is a major change in systems. One thing no one has mentioned is they will take full current right up to being full, then they shut down taking current. It's almost like a switch being turned off in your alternators. You should put in protection to avoid blowing your diodes. I'm not sure you can do that without going to external regulation.

I did this upgrade in my boat, but I'm living on it. For me it was a no brainier as I had to replace all my batteries anyway. Very glad I made the switch, but your use is not the same as mine.

dj

dj,
They will only shut off rapidly if you charge them up to the point where the BMS needs to go into protection mode. As long as your charge voltage is low enough, usually around 14.2v with decent balance, the power output will gradually decrease until very little is being produced. On my boat, I have only had one Over-Voltage-Protection (OVP) cutoff in the two years my battery has been installed. That was during testing and setup. The other way to avoid Diode Boom is by always having a FLA battery connected. I do this with the start on FLA and the house on LFP. That way the LFP can shut off without any problems because the start battery is always connected.
On Papillon, the loads on the start battery are completely seperated from the loads on the house and the FET based isolator only connects them each to the alternator but never to each other. I do have an emergency interconnect that will allow me to manually and temporarily connect the two so that I can jump start the engine in case of a dead FLA start battery.

 

[Hayden Watson]

As @Hayden Watson points out, the charging profiles for LFP and LA are different and it is easy to build a system that under charges the LA battery or over charges the LFP, both bad. Hayden has opted for a manual way of ensuring the start/reserve battery is frequently charged. I'm much too absent minded to rely on a manual system, however, I do want the ability to override any automatic system.

On my boat there is no difference in the LFP and LFA charge profile. The charge profile for my LFP is the same one that I have been using on my Group 31 AGM start battery since I purchased it in 2009. My externally regulated alternator is set to bulk charge to 14.2v and then absorb at that voltage for 30-minutes. It then drops to 13.8v for float. The reason that the FLA can get under charged is not because of the profile. It is because if the house LFP is not nearly full, the output voltage will not come above 13.4v. This will charge the start battery but will not fully top it off, so it does not cause the any problems with starting the engine. The only time that I ever worry about topping off the AGM is coming back to the dock after a long cruise but most of the time that is not even needed because I typically need to motor for several hours home and that tops off the LFP, so the AGM also gets topped off.

However there are a couple of downsides to charging the LFP directly from the alternator, a BMS (Battery Management System) dump and heat. A BMS Dump occurs when the BMS shuts down the battery while the alternator is running, this causes a huge voltage spike which fries the electronics in the alternator.

In my experience, the BMS has not been an issue as long as the battery is reasonably well balanced. Most internal regulated alternators charge to 14.2v and unless the battery is badly out of balance, the alternator will shut down charging well before the BMS needs to cut it off. That said, I do not trust my alternator to the whims of the BMS and the balance of the cells. That is why on my boat, I connect the AGM [which cannot be disconnected from the alternator] and the LFP [which can] by means of the Victron ArgoFET battery isolator. It is automatic, works all of the time and provides the full output of the alternator to both batteries based on how much each of them can take. It will never over charge either battery and will not allow one battery to discharge into the other.

There is a simple and a complex work around for this problem. As mentioned earlier heat buildup is a problem not as easily solved.

Heat buildup can definitely be a problem and is the issue that has taken the most of my time in overcoming. That does not mean that it is difficult to overcome. The steps are fairly simple.

• Increase the air-flow in the engine compartment. [I have the bilge blower exhausting hot air and a forced-air cool air duct that blows cool air from outside of the engine compartment right on to the rear of the alternator.
• If you have an external regulator, use one that has the ability to limit the power output based on the alternator case temperature. There are several nice ones available with the WS500 being the best of those.
• If you do not have an external regulator, install a thermal switch as shown in the video I posted earlier.

So, for alternator output the question is send it to the start/reserve bank or directly to the LFP bank? If sent to the LA start/reserve bank, the alternator is well protected, and the start bank is always charged at the expense of rapid charging of the LFP bank. If sent to the LFP bank first, then the alternator needs protecting and a way of charging the start/reserve bank is necessary, for the benefit of rapid charging of the LFP bank and reduced engine run time for charging.

For me the answer to the above question is "Send it to both" and reap the benefits of both options with few downsides that are easy to work around.

 

[dLj]

dj,
They will only shut off rapidly if you charge them up to the point where the BMS needs to go into protection mode. As long as your charge voltage is low enough, usually around 14.2v with decent balance, the power output will gradually decrease until very little is being produced. On my boat, I have only had one Over-Voltage-Protection (OVP) cutoff in the two years my battery has been installed. That was during testing and setup. The other way to avoid Diode Boom is by always having a FLA battery connected. I do this with the start on FLA and the house on LFP. That way the LFP can shut off without any problems because the start battery is always connected.
On Papillon, the loads on the start battery are completely seperated from the loads on the house and the FET based isolator only connects them each to the alternator but never to each other. I do have an emergency interconnect that will allow me to manually and temporarily connect the two so that I can jump start the engine in case of a dead FLA start battery.

I realize that, but it only takes once and you need to replace your alternators.

By having the lead acid set up the way you do, how do you know State Of Charge?

I run all power in and out via my lithium house bank. That way I can measure what my state of charge is. My lithium batteries charge my AGM start and my two AGM now thruster/windlass batteries. Those are maintained at full charge always as I have dedicated circuits charging those systems off my house bank. So when my charging is stopped into the system, the lithium batteries still charge the AGMs. And all is monitored so I always know my SOC if my house batteries. My solar and my wind gen also go in via the same method so all inputs are measured and all out puts are measured giving me high transparency of my house SOC.

I can't see how you can do that with what you describe.

dj

 

[Maine Sail]

This article will help...

Drop-In LiFePo4- Be an Educated Consumer

 

[SoSound]

Our existing 210 Ah FLA batteries get us probably 85% - 90% of the way to where I would like to be. The bad part about either improving energy efficiency, or adding capacity, is that you always find another way to use that newfound or added power. The last time that I took stock of what our power needs were was when I added the flexible solar panels and discovered that 20 or so additional Ah of battery would fit in my existing battery boxes. At that time, I created a list that totaled about 80 Amp Hours per day. Noticibly absent from that list is the power hogging forced air heater... I'll have to look that information up when I get home again. I have a note on my list that I would need capacity equal to 4 times my list of "requirements", or 320 Ah. I also made a note that I'd need "at least 240 Ah"... I'm not sure if I meant that to say that I would be willing to settle for 2/3 of what my research at that time told me that I would need, or if it was a best case scenario vs. an acceptable capacity. Whatever it meant, I still only managed to install 210 Ah of total capacity. What it tells me, is that there is insufficient capacity to operate on batteries alone, and I'm still looking to improve on that. FWIW, my top power consumers are; Refrigeraton, Chart Plotter, Auto Pilot, Instruments, Nav Lights, VHF. Not too many luxury items there, and from the bottom of that list the individual items drop off dramatically to just a few amps per day. On the other hand, if we stay two days in a destination, then we are not using any of the top power consuming navigaition related items on that list for a day and the power requirements and recharging begin to even out.

Another way of looking at my situation, is to say that I have limited space available (physically replace my two group 31 house batteries), and ask what LFP options are available to fit that space. If I find a physically acceptable LFP replacement, then what would I need to alter to charge the new LFP house bank?

If my potential replacement battery bank is physical space limited, then will my 120A alternator still be as big of a problem as it appears at first glance? If my physical space limits me to a hipothetical 400 Ah of LFP battery capacity, and I use 80 - 100 Ah per day while away from the dock, will my alternator, solar, and shore power charger be able to keep up with that level of demad? If not, is it possible to prioritize the charging system upgrades?

I like the idea that making the transition to LFP is something that might be accomplished over a couple of years, if necessary.

 

[Hayden Watson]

I realize that, but it only takes once and you need to replace your alternators.

I agree, which is why I have the ArgoFET so that there is no way that the alternator will ever be without a battery to put the power into.

By having the lead acid set up the way you do, how do you know State Of Charge?

My lead acid and LFP are completely electrically separated with no current passing from one system to the other. Due to the FET based isolator, there is a connection from the alternator to the LFP house AND a connection from the alternator to the FLA start. Because it is FET based and not the older Diode based isolator, I have almost no voltage drop across the connection. I sense the voltage at the alternator terminal on the ArgoFET but my cables are all 2/0 so I am not worried about the voltage drop I will get in the wires to the battery.

I do not worry about the SOC of the FLA other than to have it charge at 14.2v for long enough to get it topped off. That is no different than what I have done on this boat since I got it in 1998. I do not know the SOC of any start battery I have ever owned so do not figure that I need to know now.

I run all power in and out via my lithium house bank. That way I can measure what my state of charge is. My lithium batteries charge my AGM start and my two AGM now thruster/windlass batteries. Those are maintained at full charge always as I have dedicated circuits charging those systems off my house bank. So when my charging is stopped into the system, the lithium batteries still charge the AGMs. And all is monitored so I always know my SOC if my house batteries. My solar and my wind gen also go in via the same method, so all inputs are measured, and all out puts are measured giving me high transparency of my house SOC.

How do you measure the amps that go out of your house bank and into your AGMs?
On the LFP bank, I have the SOC listed on the BMS which is suspect as to its accuracy but gives an idea of capacity. My primary means of tracking it is with a shunt-based battery monitor that is connected to the battery between the BMS and the negative charge buss. It counts all amps in and out regardless of the source or load.
Because shunt on the LFP battery negitive it only counts the amps that go to the LFP from the isolator. It does not count any amps that go to the start battery which as I said before, I do not care about. I am only interested in the amps that I have to use and replace to the house. The only monitoring I do to the start battery is to monitor whether it starts the engine or not. If not, I check the battery for capacity. So far, this one has been starting every time with 10-15 seconds of glow plug on even the coldest days.

I can't see how you can do that with what you describe.

I cannot see what I am missing.

• I have protection for the alternator with a continuous charge path.
• Battery monitoring for the house bank of all power used and replaced.
• Proper charge voltage for both battery banks.
• No need to remember to do anything to make it operate.

 

[Stu Jackson]

At that time, I created a list that totaled about 80 Amp Hours per day. Noticibly absent from that list is the power hogging forced air heater... ............ I still only managed to install 210 Ah of total capacity. What it tells me, is that there is insufficient capacity to operate on batteries alone, and I'm still looking to improve on that. FWIW, my top power consumers are; Refrigeraton, Chart Plotter, Auto Pilot, Instruments, Nav Lights, VHF.

Dave, Your energy budget and storage is way out of whack. Look, 99% of marine refrigerators use 60 ah per day. Period. It is a "given" that's been supported by real world input and reality for over four decades. My boat is pretty much the same as yours, 34 feet, with an Adler Barbour fridge. I did three energy budgets back when I bought the boat in 1998: anchor, daysails, overnight sails. As you note, they are three different numbers. But the reality is, in your case, that your desire (i.e., to stay longer at anchor without recharging) are impossible because you energy storage is woefully inadequate, by a factor of 2. Again, as discussed for decades on this and other boating forums, a basic battery storage for FLA - old school chemistry, wet cells or AGM - has said that with a fridge the bare minimum is 400 ah house bank of which 200 ah is usable. It is simple math: 60 ah fridge plus "the usual stuff" plus phones and laptops = 100 to 120 ah per day AND assume you motor a little to get to your anchorage and figure your house bank is full when you drop the hook, you get two days or nights. That's it. With your house bank you only get one. I have an energy monitor and have seen this at anchor for years. It is true. 100-120 ah per day, same use as you. But that's BEFORE your heater!!!

The All-Important Energy Budget:
Energy Budget

The beauty of LiFePO4 is that you can use more than 50% of the bank capacity, figure say 80%, so the same nominal 400 ah bank will give you 320 usable ah instead of 200. Maine Sail explains it all in his excellent link which he wrote years ago.

then will my 120A alternator still be as big of a problem as it appears at first glance? If my physical space limits me to a hipothetical 400 Ah of LFP battery capacity, and I use 80 - 100 Ah per day while away from the dock, will my alternator, solar, and shore power charger be able to keep up with that level of demad? If not, is it possible to prioritize the charging system upgrades?

An internally regulated alternator with LiFePO4 will not work. The reason is that LiFePO4 batteries have a much higher and almost continual acceptance,, meaning they can and will take more amps in throughout their entire charging period. Your alternator will burn up! Maine Sail also covers the requirement to revisit your entire charging system.

 

[Hayden Watson]

If my potential replacement battery bank is physical space limited, then will my 120A alternator still be as big of a problem as it appears at first glance? If my physical space limits me to a hipothetical 400 Ah of LFP battery capacity, and I use 80 - 100 Ah per day while away from the dock, will my alternator, solar, and shore power charger be able to keep up with that level of demad? If not, is it possible to prioritize the charging system upgrades?

I like the idea that making the transition to LFP is something that might be accomplished over a couple of years, if necessary.

From what I can see, your only real problem will be how to control your alternator. If you do not do anything to modifiy it, I would suspect that you will need to add a DC 2 DC charger to take amps from the start battery to charge the alternator. I personally would not want to go that way becasue it greatly reduces the amps you have to recharge your FLP bank. Most of the D2D chargers are only 30A-40A so you are a long way from what you are making with your 120A alternator.

If I had your set up and did not want to pop for a new alternator and regulator, I would look to either converting the alternator to external regulation or putting a thermal switch to let it stop producing to allow it to cool if it gets too hot. Either of those are easy to do.

Your shore and solar chargers will just need to be programmed for the correct voltages.

Your isolator should keep your lead and LFP on speaking terms across a nice strong fence.

 

[SoSound]

I have an energy monitor and have seen this at anchor for years. It is true. 100-120 ah per day, same use as you.

Sounds like a recommendation for a ‘priority’ upgrade. If I am not finding or compiling the data for estimating my power requirements, then measure what I’m actually using. I remember raising an eyebrow when I saw the fridge‘s draw in amps, I’m guessing at the number of hours it runs.

 

[Stu Jackson]

Dave, Hayden is right. I just re-read Maine Sail's excellent article again for like the tenth time! Maine Sail covers ALL of this, ALL of it. One of my favorites is about your stock alternator and internal regulator. Your alternator WILL burn up connected to a LiFePO4 bank. And he shows some pictures of what it looks like.

YOU MUST read the link in its entirety. Then read it again a few more times. Clear enough? The reason I stress this is that it is tiresome dealing with reinventing the wheel stuff when the answers not only are out there, but have been presented. Hayden did his homework, as have others here who are trying to help you.

There's also a complete lithium sub-forum over at www.cruisersforum.com. Trust a contributor named jedi and a few, very few, others. It's well worth your time to noodle around over there.

Good luck.

 

[Hayden Watson]

FWIW, on my C30 I use an average of 100Ah per day for 12v AB icebox conversion, 50L freezer, 2-hours of hydronic heat each morning and all other normal loads. This is based on the monitored amps used on four 7-10 day cruises in the past two years. One thing that surprised me was that my amps used went down when I switched to LFP from AGM. This is because the power used is actually watts which is amps times voltage. The AGM was always in the range of 11.5v to 12.6v. The LFP is never below 13.2v. This means that an appliance that consumes 100Wh of energy will use 8.7A - 7.96A on the AGM. The same 100Wh load will only use 7.57A for a 5%-15% reduction in the amps consumed.

 

[Stu Jackson]

Sounds like a recommendation for a ‘priority’ upgrade. If I am not finding or compiling the data for estimating my power requirements, then measure what I’m actually using. I remember raising an eyebrow when I saw the fridge‘s draw in amps, I’m guessing at the number of hours it runs.

Dave, maybe, maybe not. I've had my monitor since 2003. What I've found is that if done properly an energy budget is usually correct within +/- 5%. That means the budget ALONE is superb in figuring out what is going OUT of your house bank. Where the monitors truly SHINE is when you're off grid and are dependent on what is going back in. Because of lead acid battery technology, called battery acceptance, as lead gets recharged its ability to accept charge starts dropping. Dramatically. Not so for LiFePO4.

Essentially you don't NEED monitor to learn what's going out, but you do NEED it to learn what's gone back in when you are away from shorepower. Most everyone would agree it's a good thing to have. The best shunt monitor is the Victron BVM series.

But please, before you start jumping, continue to do your research - you have the winter to do it, right?

You might enjoy noodling around this link, which doesn't "do" LFP but covers much of everything else on boat electrical systems.

Electrical Systems 101 Electrical Systems 101