Dead Battery Bank

[Xfirepop]

Rookie captain here with a basic electrical question. The picture below shows my battery banks. I'm wondering which banks do what. The lower 8L16 bank is dead, 12 volts, thus the charger kicked off and won't bring them up. I already knew they were on their way out, just not this quick. Is this lower bank my starter batteries or are they the house, deep cycle, batteries? All 12 volt items on the boat are dead, not enough juice to run them.
My question is do I replace them with exactly the same or can I switch to a set of 31M batteries?

 

[mvweebles]

The bank at the bottom of the picture is four 6v batteries so very likely your house bank. If they are truly dead, consider replacing with 6V golf cart batteries - Costco/Sams carries them for a bit over $100 each.

But the bigger issue is why did you lose charge? I see seven batteries in the picture - guessing the three upper ones are two for engine start, one for generator? Having them all go south at same time seems like too much of a coincidence.

There are much better folks on this forum with electrics than me so I won't muddy the water except to say you might want to try disconnecting each battery and charging it in isolation to see if it is spent. Given replacing the all batteries will cost close a grand, you might want to cough-up $75 for a decent load tester to see if each is in good shape.

Peter

 

[Mac2]

Looks like the upper bank has two agm's mixed in with the wet lead acid batteries. A lot of guessing without knowing where the cables go, but it looks like the wet batteries on the bottom picture are the house batteries. The battery bank at the top looks like starting batteries. The two agm's going to a main engine(s) and the remaining wet battery going to a generator. You need to trace the cables regardless, so you might as well do it now. I did the wet batteries for years and finally got smart and switched to lifeline agm's.

 

[Xfirepop]

As usual, you guys are right on. The two AGMs are wired seperate from the lead acid one. Those three are holding a charge, its the lower four that are dead. The specific gravity tests have been going south for a while. Each battery at a different level (?) so I knew they were going bad. 8 yrs old not too bad for lead acid. Thanks for the clarification, I had it backwards I thought the lower batteries were the starter batteries, Now it all makes sense. I'm going to replace them this coming week. Can I use 31M AGMs instead of those suitcase monsters? At 75 yrs old I do try to eliminate heavy items in my life!

 

[Mac2]

As usual, you guys are right on. The two AGMs are wired seperate from the lead acid one. Those three are holding a charge, its the lower four that are dead. The specific gravity tests have been going south for a while. Each battery at a different level (?) so I knew they were going bad. 8 yrs old not too bad for lead acid. Thanks for the clarification, I had it backwards I thought the lower batteries were the starter batteries, Now it all makes sense. I'm going to replace them this coming week. Can I use 31M AGMs instead of those suitcase monsters? At 75 yrs old I do try to eliminate heavy items in my life!

Yes. Just make sure you wire properly i.e. all parallel battery cable connections are the same length and the two main cables going to your inverter/charger are hooked on opposite ends (positive on one end and negative on the other end). If not, this could explain the different readings you’re getting now.

 

[Antares]

With 8 year old batteries they probably need replacement. I had a similar situation but with a new bank of 8 golf cart batteries. I lost shore power during an extended trip and my less than an year old house bank was flat, less than 1 volt. My smart charger wouldn't charge them at all. Frustrated I read the manual for the charger and discovered there was a minimum voltage below which it would not charge. I went to the closest car parts store and bought a dumb charger. In a few minutes the voltage was high enough to trick the smart charger to kick in. So far this summer the bank is doing ok. It probably will need replacing sooner than usual but until then I'm thankful its doing the job.

 

[ranger58sb]

My question is do I replace them with exactly the same or can I switch to a set of 31M batteries?

I can't make out pics as well as others have...

But if the top three batteries are your engine (one for each of 2?) and genset start batteries...

And if those are maybe 8Ds or some such...

I'd first look at your engine's recommended minimum CCA/MCA requirements... and then compare that to specifically to Odyssey Extreme ODX-AGM31s (with your choice of connector type), 1150 CCA... because with those you might be able to replace each 8D with a single Odyssey 31.

If that third battery in the upper bank is also an 8D... for a genset?... that'd be another opportunity to downsize BCI group without compromising starting ability. (Or maybe that's for a thruster or some such? If so, maybe a pair of those AGM31s...)

Were it me, I'd probably also make all the others AGMs, too, to eliminate watering chores (more expensive, in money; less expensive, in "chore time"), reduce self-discharge rate, and reduce off-gassing in the battery compartments. Probably Lifeline GPL-4CTs for the house bank.

Given your house bank seems to be completely separate from starting or thruster loads, it would be a decent time to compare a LiPo solution, too.

-Chris

 

[Bmarler]

I’m with Peter, why are they dead? Did the charge source fail and they just ran themselves down?
Before I would think about replacement, I’d bring in a “dumb” charge source and bring them up to a reasonable level. Then, I’d pull the cables, and clean them up as well as the battery connections. Check the specific gravity when everything is disconnected and record the values. Then, hook everything back up, run an equalize cycle. The equalize can even out the differences in specific gravity and rejuvenate the cells.
I wouldn’t change the cabling arrangement, I think you’re pulling from a good spot. When you tap the ends of the bank, the center doesn’t load as heavy. Tapping off center and opposite locations like you are is a good method.

 

[Mac2]

I wouldn’t change the cabling arrangement, I think you’re pulling from a good spot. When you tap the ends of the bank, the center doesn’t load as heavy. Tapping off center and opposite locations like you are is a good method.

If you tap into one end of the house bank with the negative and the other end with the positive, you are pulling power through the entire bank evenly. Unless of course this thought process has changed. Anyone else have thoughts?

 

[dhays]

The house bank batteries have a manufacture date of 8/17. So they are 7 years old and frankly look a bit beat up. I would take a look at your charging system to be sure that what you replace them with, are charged as recommended by the manufacturer. Check to see if you have at least a three stage charger and it is properly setup and and functioning.

Your two other banks seem to be a pair of 12v SLA batteries in parallel and then a single 12v FLA battery. Likely as old or older than the House bank. To find out where they are connected, you will need to follow the wire. Not sure if it is common to have a single bank used to start two engines? I've never had a twin.

I have a L16 house bank in my boat. They can be a pain to move, but aren't bad if you can lift from directly above them. If there is room, two folks can do it pretty easily so replacing like for like would be a simple job with a helper (any grandkids around?). As near as I can make out, the battery bank was wired well so I don't think that is the cause of the voltage difference between your batteries.

GC2 6v batteries are easier to move, but won't fit the same enclosure. I don't think you will fit Group31 batteries in that same enclosure either.

As noted in another recent thread, when I replace my L16 house bank, I will likely replace with LiPo. I would look at that option. If you are going to change the enclosure anyway.

 

[Bmarler]

If you tap into one end of the house bank with the negative and the other end with the positive, you are pulling power through the entire bank evenly. Unless of course this thought process has changed. Anyone else have thoughts?

I look at electricity like water. The tap is a drain, pulling the power closest to it first and nearby cells shedding power towards the new low area created by the drain. So I put my taps near, but not on, the ends of the bank, and at opposing locations for positive and negative.
My house bank is ten batteries, I think it can make a difference where I tap vs a smaller bank. Cross connecting would be an improvement, but my bank is linear down the bilge space, so inconvenient.

 

[dhays]

My house bank is ten batteries, I think it can make a difference where I tap vs a smaller bank. Cross connecting would be an improvement, but my bank is linear down the bilge space, so inconvenient.

It may be inconvenient, but I think it can make a significant difference. Check out this article. It explains it well.
Battery connections

 

[Mac2]

This is what Im referring to. I see diagrams with your technique as well.

 

[Bmarler]

It may be inconvenient, but I think it can make a significant difference. Check out this article. It explains it well.
Battery connections

Have read that before. And many other articles like it. Good stuff there.
My setup is similar to the #4 design, but with a little more complexity as there are more batteries.

 

[dhays]

Have read that before. And many other articles like it. Good stuff there.
My setup is similar to the #4 design, but with a little more complexity as there are more batteries.

yeah, 10 batteries is a lot to manage.

 

[BruceK]

I don`t see a mystery. The 4 batteries are 8 years old connected as one battery. One sick battery (or cell) of the 4 calling for charge can lead to constant unsuccessful charging attempts. It will deplete its companions too. Seems judging from the white powder at least one has been "boiling" off electrolyte. If they were sealed types one might have exploded. Don`t overthink it, just replace the bank.

 

[Xfirepop]

Thanks for all the advice! As usual, you guys not only answered my questions, but went beyond and gave me advice to improve my situation. Thank you. With your info I'm going to replace those dead batteries with 4 Lithium Phosphates and wire them in according to the mentioned wiring diagrams. Thanks again, Richard B

 

[SteveK]

Thanks for all the advice! As usual, you guys not only answered my questions, but went beyond and gave me advice to improve my situation. Thank you. With your info I'm going to replace those dead batteries with 4 Lithium Phosphates and wire them in according to the mentioned wiring diagrams. Thanks again, Richard B

Be sure to confirm your sources for charging the LifePO4. Do you have them, or what you need to do or add.