Currently have 405AH with two group 31s and one 4D wet cell batteries, plus separate starter battery. They're only 2 years old, but the house bank no longer holds a charge. My fridge cold plate draws 4.5A and everything else 2.5A-4A. I get 40Ah a day ave from solar recharging and run the engine for an hour each morning and evening. Last 2 seasons this worked great, but now the house bank won't output more than 12V for about 4 hours. I expected at least another year from these batteries. What's the recommended replacement batteries? I use 150-200AH per day
Replacing House Batteries on Hunter 40.5
- Thread starter S.V. Windshadow
- Start date
I would first research your battery wiring and charging setup. Two years life is way too short.
While we do not live aboard, we do run the fridge all season and when we typically cruise for 2 to 4 weeks in the summer we can count on anchoring out for 48 hrs and then starting the engine off of the house bank. Our boat is smaller, so our house bank is a pair of Trojan GC batteries. We are on our second set, having gotten 9 years out of the last set.
For an emergency we also have an Optima 12 volt battery (AGM), I should note. It gets tested several times a year. It never grows weary of waiting patiently for a call to duty....
My battery guru's all say that a bank should last at least 5 years, minimum. (FWIW)
While we do not live aboard, we do run the fridge all season and when we typically cruise for 2 to 4 weeks in the summer we can count on anchoring out for 48 hrs and then starting the engine off of the house bank. Our boat is smaller, so our house bank is a pair of Trojan GC batteries. We are on our second set, having gotten 9 years out of the last set.
For an emergency we also have an Optima 12 volt battery (AGM), I should note. It gets tested several times a year. It never grows weary of waiting patiently for a call to duty....
My battery guru's all say that a bank should last at least 5 years, minimum. (FWIW)
Battery arrangements differ boat to boat as they were done upon commissioning. I have four AGM golf carts that measure about 400 AH/day. Starting battery is separate, but also AGM. I use about 110-120 AH/day used carefully. That includes both the frig & freezer which is about 80-90% of the current draw. I have 200 watts solar which runs everything during the day. Add to that a one hour run on the Honda 2000. I am adding another 200 watts solar with the hope to be largely generator-independent. My house batteries are located in the aft cockpit lockers, two per side. As to life, I generally get three to four years out of the house bank. Hope these AGM's last a bit longer.
What size alternator do you have and how is it regulated? It seems like if you burn 200AH per day and only get 40 back from solar you probably aren't getting enough out of the engine to approach 100% SOC. Over time sitting below 100% is probably reducing life expectancy. What do your voltages look like after the engine runs?
For most of us, an AGM house bank is a poor choice, expensive with a short life span. The advantage to AGMs is that they can accept high rates of charge, but they need a high output alternator and a high output battery charger. If they are left in a partial state of charge, PSOC, they die an early death. Practical Sailor and Rod Collins just published a piece on this (available without a subscription): https://www.practical-sailor.com/bl...ailor:e38341:177032a:&st=email&s=p_Blog081618
AGMs work for dedicated start batteries because they are never deeply discharged and are brought back up to 100% SOC quickly because they are not deeply discharged.
Regularly taking batteries below 50% SOC will shorten battery life, they like being at 100%. In your case with brand new fully charged batteries you start with 405 Ah. With a 200 Ah per 24 hour draw, after one day they are at 50%. After charging with 40 Ah from Solar and maybe another 100 Ah from running the engine only 140 Ah have been put back at best. The battery capacity is now at 345 Ah or 85% of the original Ah capacity. On Day 2, another 200 Ah are drawn out, leaving the battery at 145 Ah or a 35% SOC. Putting back 140 Ah leaves the battery with 285 Ah or at 70% SOC. Keep repeating this cycle and pretty quickly the batteries are dead. Your actual numbers may vary some, but this is the pattern.
Some questions to consider:
How are the batteries connected? Are the 3 batteries connected as on big bank in a series/parallel configuration? If so, they should all be of the same type, brand, and age.
How are you monitoring the SOC? How are you monitoring charging rates?
What kind of alternator and regulator do you have? Internally regulated, stock automotive type alternators do a poor job of recharging large house banks. A high capacity externally regulated and temperature compensated alternator will do a better job.
What kind of solar controller are you using?
Finally, with all things electrical, go to MarineHowTo.com and devour the articles on charging, batteries, and alternators.
AGMs work for dedicated start batteries because they are never deeply discharged and are brought back up to 100% SOC quickly because they are not deeply discharged.
Part of the problem is the batteries are not reaching a 100% state of charge. Charging is not as simple take out 40 ah and put back 40 ah. The charge acceptance rate decreases as the SOC increases. Thus, if 40ah are taken out it may take 60 ah of charge to bring them back to 100%. There are formula's to calculate this, google Peukert effect.
Regularly taking batteries below 50% SOC will shorten battery life, they like being at 100%. In your case with brand new fully charged batteries you start with 405 Ah. With a 200 Ah per 24 hour draw, after one day they are at 50%. After charging with 40 Ah from Solar and maybe another 100 Ah from running the engine only 140 Ah have been put back at best. The battery capacity is now at 345 Ah or 85% of the original Ah capacity. On Day 2, another 200 Ah are drawn out, leaving the battery at 145 Ah or a 35% SOC. Putting back 140 Ah leaves the battery with 285 Ah or at 70% SOC. Keep repeating this cycle and pretty quickly the batteries are dead. Your actual numbers may vary some, but this is the pattern.
Some questions to consider:
How are the batteries connected? Are the 3 batteries connected as on big bank in a series/parallel configuration? If so, they should all be of the same type, brand, and age.
How are you monitoring the SOC? How are you monitoring charging rates?
What kind of alternator and regulator do you have? Internally regulated, stock automotive type alternators do a poor job of recharging large house banks. A high capacity externally regulated and temperature compensated alternator will do a better job.
What kind of solar controller are you using?
Finally, with all things electrical, go to MarineHowTo.com and devour the articles on charging, batteries, and alternators.
...and proper discharging, charging, and storage. Meaning, besides properly watering them, they shouldn't be discharged past 50% capacity, nominally about 12.1V; they should be fully charged, if at all possible, which can take a long time; and they shouldn't be left at much less than full charge. For example, if you are a weekend boater and not plugged in, charge them before you leave the boat Sunday evening. Solar can solve a lot of these issues.
That said, if you have the height in your battery compartment, the industrial flooded deep cycle batteries are the best, in my opinion. You can even get 'automatic' watering systems, i.e., connect a tube to a water source via a bulb, squeeze the bulb until it's firm, and your batteries are watered.