"Powersport" and Lawn and Garden Tractor Batteries as Starting Batteries

[jviss]

Greetings,

I brought up this topic a few years ago, and I'm considering it again, for my "new" boat.

On the Catalina 36, with Universal M25, based on the Kubota small tractor D850, I researched the size of the battery they put in the tractors in which most of these engines shipped, and that's what I put on the boat as a starting battery. Worked like a charm, and only weighed about 12 lb. Would start the engine innumerable times without a charge!

Now i have a 4 cylinder Westerbeke 38Hp diesel that's a Misubishi. I don't know what tractor this one is from. But, I'm considering a 180CCA AGM that weighs about 12lb. as a starting battery.

Has anyone else thought along these lines, or even done this?

Thanks,

jv

 

[dlochner]

A small battery may work OK for starting, but it will not have very much usable capacity as a reserve battery in case of house bank failure.

Give the lack of reserve power I see no advantage to saving 60 lbs on a 15, 000 lb boat by using a small battery.

 

[jviss]

Agreed, Dave, I'm not expecting the starting battery to run the house. The weight issue is, lately, me trying to get that battery on and off the boat each off-season! I mean, not a terrible burden, but a bit of a pain.

(more in a bit)

 

[dlochner]

Agreed, Dave, I'm not expecting the starting battery to run the house. The weight issue is, lately, me trying to get that battery on and off the boat each off-season! I mean, not a terrible burden, but a bit of a pain.

(more in a bit)

My batteries go in when they are new and leave when they are past their prime. Cold is good for battery life so long as the battery is fully charged and disconnected from the system.

Save your back, leave them on board. When it is time to change them, do it after launch so they don' have to go down a ladder.

 

[jviss]

I'm so torn and confused about batteries lately. I really want a big LiFePo4 house bank, and would probably keep an AGM starting batt to which to connect the alternator.

 

[dlochner]

I'm so torn and confused about batteries lately. I really want a big LiFePo4 house bank, and would probably keep an AGM starting batt to which to connect the alternator.

The question I always ask, either implicitly or explicitly, is why do you want to do whatever. So I'll ask that question of you, why do you want to have a big LiFePO4 bank?

 

[Benny17441]

My take on dedicated starting batteries is to be able to have one compatible with those on the House bank to provide redundancy. Deep cycle batteries can easily crank those small diesel engines and also simultaneously serve as back up power for the House battery bank. Those small tractor batteries are only adequate to start the engine. Whether a battery weighs 12 lbs. or 70 lbs. does not make much difference to the boat's performance. Starting batteries do not take very kindly to deep discharge cycles as they are designed with lighter lead plates to produce large bursts of power for a short duration. By contrast the deep cycle batteries are design to provide a large number of charge/discharge cycles over their useful life.

 

[jviss]

I'm going to start a new thread on backing up the house bank (or maybe not), as that's where this one's headed. I really wanted folks' input and experience with a dedicated starting battery.

My thinking lately is the best backup for a house bank would be a compact battery with really good storage life, a Lithium battery of some kind, left charged to 85% (best for Lithium battery life). As a matter of fact, maybe more than one of these, like one for 'vital' gear like radio and GPS, another for autopilot, another for 'generic' house loads. If the main house fails, shut off the fridge, for sure!

To design a house backup I would first lay out a requirement that also addresses failure modes of the house, how it's recognized, how it's remediated, and for how long the backup must persist, with what loads. First might be to shed some load, like the refrigerator. Then prioritize the loads, and determine how long you will need the backup before the main house failure can be repaired.

I frankly don't know the various battery failure modes off the top of my head, and I'm sure it varies based on battery chemistry. I also don't know how often this happens. Has anyone experienced a main back failure? If one battery of a multiple battery bank fails, do you have a way to detect this, and a way to isolate it?

If it's just accidentally running the main bank down to nothing, that's another story, another 'failure mode.' One way to avoid this would be load-shedding low-voltage disconnects with alarms. Shed fridge at 20% of useable capacity, autopilot at 10%, or something, and so on. The alarm should prompt you to start the engine. Thank goodness for a dedicated starting battery!

 

[dlochner]

The more complicated you make the system the more points of failure you introduce and the more difficult it will be to troubleshoot.

I have no real data, just anecdotal, the primary cause of battery failure is human, drawing the battery down too low, improper charging, expecting a longer life than is reasonable, and so forth. Battery failures due to manufacturing seem to be pretty rare. After 50 years of car and boat ownership the only time I have had batteries fail has been due to age or excessive discharge.

The key to getting the most from the battery is a good monitoring system. Without knowledge of the batteries SOC and SOH it is a guessing game.

A low voltage disconnect on the major current draws (refrigeration) will help protect the batteries from being over drawn.

Isolating the start/reserve from the house battery provides a back up for essential functions (sorry, this means warm beer) and can get you home. It should take a deliberate act to switch over to the start/reserve battery, one that is difficult to do accidentally.

With LA batteries, if one battery in the bank fails, the bank fails until the bad battery is removed. The good batteries will keep trying to charge the dead battery until all are dead.

Keep it Simple.

 

[jviss]

As far as I can tell, from internet research, the vast majority of flooded lead acid battery failures are "soft," i.e., not a sudden, catastrophic failure, but a degradation of performance. If these suddenly shorted we'd have systems that protected from that in some way.

 

[dlochner]

As far as I can tell, from internet research, the vast majority of flooded lead acid battery failures are "soft," i.e., not a sudden, catastrophic failure, but a degradation of performance. If these suddenly shorted we'd have systems that protected from that in some way.

If you dig a little deeper I suspect you will most of those failures were AGMs. And those failures are almost always due to improper charging and/or leaving them in a partial state of charge.