Dead Battery Bank

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Xfirepop

Xfirepop

Veteran Member
Joined
Sep 10, 2022
Messages
28
Vessel Name
C C Rider
Vessel Make
Gulfstar 44
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?
 

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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
 
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.
 
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!
 
Xfirepop said:
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!
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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.
 
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.
 
Xfirepop said:
My question is do I replace them with exactly the same or can I switch to a set of 31M batteries?
Click to expand...

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
 
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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.
 
Bmarler said:
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.
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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?
 
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.
 
Mac2 said:
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?
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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.
 
Bmarler said:
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.
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It may be inconvenient, but I think it can make a significant difference. Check out this article. It explains it well.
Battery connections
 
This is what Im referring to. I see diagrams with your technique as well.
 

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dhays said:
It may be inconvenient, but I think it can make a significant difference. Check out this article. It explains it well.
Battery connections
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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.
 
Bmarler said:
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.
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yeah, 10 batteries is a lot to manage.
 
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.
 
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
 
Xfirepop said:
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
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Be sure to confirm your sources for charging the LifePO4. Do you have them, or what you need to do or add.
 
I've purchased the LiPO4 batteries and have begun the slow learning curve on how to properly set up the charging system for them while retaining the new AGM starting batteries. I have two 3208's with 50 amp alternators on them. Does anyone have a wiring diagram for such a system? I've spent two days searching and haven't found one. Since this will be the only time I do this install, I don't want to become an electrical engineer or expert on charging systems, I just want to do a clean and efficient install with enough of an understanding to repair any problems I might encounter. Any tips or links would be greatly appreciated. I already know I need a dc to dc charger, but one for the battery bank or two to protect each alternator? The learning curve grows longer each year on technical stuff !!
 
I'm not sure you will find a "standard" wiring diagram since every boat seems to be different.
 
Xfirepop said:
I've purchased the LiPO4 batteries and have begun the slow learning curve on how to properly set up the charging system for them while retaining the new AGM starting batteries. I have two 3208's with 50 amp alternators on them. Does anyone have a wiring diagram for such a system? I've spent two days searching and haven't found one. Since this will be the only time I do this install, I don't want to become an electrical engineer or expert on charging systems, I just want to do a clean and efficient install with enough of an understanding to repair any problems I might encounter. Any tips or links would be greatly appreciated. I already know I need a dc to dc charger, but one for the battery bank or two to protect each alternator? The learning curve grows longer each year on technical stuff !!
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You will have to first verify how the system is wired now. One alternator for starts and the other for house or a parallel connection. Is the system now wired to share house and starts? You will have some "quality time" in the engine room with tape and marker, meters, jumpers and a notebook and pencil. Yeah it's a lotta work but in the end you will know how your boat is wired - :)

Reason is even though you may fine some documentation on board or elsewhere, mods could have been done like my documentation which said I had a generator battery only to find I didn't and the suspected generator battery was instead shunted over to the house.
 
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I already know I need a dc to dc charger, but one for the battery bank or two to protect each alternator?
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You do not need a wiring diagram of how it is wired. You plan to use DC2DC chargers from the battery that the alternator of each engine is charging.
If you now have one alternator with no where to go as the old house bank was FLA and replaced, then you can run that cable to the start batteries too,
The two AGMs are wired seperate from the lead acid one.
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The two AGM can be on one ALT and the 8DFLA can be on the other ALT

The DC2DC are wired from the FLA/AGM to the new LiFePO4 batteries. You need to have an ON/OFF control (from the run position of the ignition) to the DC2DC chargers to avoid draining the start BAT when the engines are stopped.
 
Question on DC to DC charger: OP will have at least one DC to DC charger from a start battery to his house bank. Does he need to protect the alternator from burning up by adding something like a WS500?
 
Mac2 said:
Question on DC to DC charger: OP will have at least one DC to DC charger from a start battery to his house bank. Does he need to protect the alternator from burning up by adding something like a WS500?
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you protect the ALT with the DC2DC by getting one that is about 70% of the max ALT, in this case with a 50A ALT, get a 30A DC2DC for each ALT.
So far I have not burned up my ALTS.

Of course if you want to get an external regulator even better. I doubt those 50A ALTS can be converted so that means new ALTS.
 
SteveK said:
you protect the ALT with the DC2DC by getting one that is about 70% of the max ALT, in this case with a 50A ALT, get a 30A DC2DC for each ALT.
So far I have not burned up my ALTS.

Of course if you want to get an external regulator even better. I doubt those 50A ALTS can be converted so that means new ALTS.
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So I guess my question would be can those alternators run continuous at 70%? Also, what conversion do you need to hook up a standard alternator to a WS500?
 
I did some digging and found that 8D agm batteries AND the 8L16 batteries are both house banks. The starter battery is the lonely 8D lead acid. Both alternators are linked and charge the entire system from one feed, the 8Ds first then thru to the 8L16s. So does that mean I need to run down the point where the alternators are linked and put a 12v to 12v charger on each one. Each alternator is putting out 50 amps and I can't find a 70 amp 12v to 12 charger for the combined amps. I do have a set of three Perko battery switches that let me chose routing of input and output of each bank. 20240721_120229.jpg
 
Batteries usually don't go absolutely dead where they won't run anything while a charger is on. I'd look for a reason before putting in new batteries. Cable connection, an appliance that draws power while off, are you going thru zincs too fast, etc.
Unless isolated, all batteries in a charging bank need to be the same size and same capacity. No low cells, etc. Even then the charger will only charge the batteries that reach full first, leaving the others at a lower charge. You can replace with any 6v or 12v combination you want, but may not have the same capacity you had when the old batteries were new. 6v and 8d batteries have more capacity because they have larger and thicker plates.
 
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