House Batteries got hot

My house battery bank consists of 3 group 31 deep cycle exide nautilus lead acid batteries paralleled together with the positive to the boat on one end of the bank and the negative on the other. I also have a watering system that I can plug in a hose to water the batteries without having to remove the caps and fill the individual cells. 2 of the batteries are watered through one hose and the other has a separate hose.



The middle battery was essentially dry when I found the problem due to the sulfur smell. The other 2 were gassing excessively. All 3 measured 160 deg F with a laser thermometer. My inverter/charger puts out about 60 amps at peak bulk charge. This happened after I came home and plugged in so I'm ruling out an alternator issue. As a side note - I had noticed the sulfur smell a few weeks ago also and thought it was my waste tank. And the batteries had been drained probably close to 100% a few weeks before this as I forgot to switch on the shore power and the inverter powered the refrigerator and freezer until the lower voltage limit of the inverter kicked in.

I´m thinking that the center battery was low on water as it is the second in line for the watering system and when I filled the batteries it did not get filled - just conjecture on my part. When I plugged in the inverter it went to max since the batteries were low from running the refrigerator and freezer off the batteries the night before. With the compromised center battery the inverter kept pumping 60 amps into all 3 and the 2 outer batteries tried to compensate. Then they all started to rise in temp due to the overload.

In addition, the only other possible contributor could be that the neg going to the engine might have been loose. I disconnected the batteries to let them cool and can´t remember loosening that lead and then when I went to remove the batteries - found it loose on the terminal that is a separate post from the other neg leads. The lead to the inverter and parallel leads were all clean and tight.

This event scared the hell out of me. I thought the batteries were about to blow up or catch on fire and if I had not found it when I did - I´d of probably lost the boat. I´m thinking of adding a temperature alarm for the battery box.

Any comments or suggestions.

Well, when the middle battery went dry it was probably a result lead sulfate accumulating in the bottom which shorted the plates. Shorted plates is what makes a battery run hot. If the other batteries are running hot too they are probably shot as well.

Replace all of the batteries and pay better attention to electrolyte level. FWIW while living aboard full time I only had to add water 3-4 times a year to my golf cart batteries. With good batteries and a good charger, batteries don't use that much water.

David

Consider replacing with AGMs.

When one battery in a parallel set goes bad the other try to maintain the parallel voltage by pumping charge into the bad battery. It gets hot and boils acid. They all overheat from too much current. Batteries have melted and caught fire in this manner.
The type of battery does not matter parallel batteries have this built in failure mode. The strong try to prop up the weak.

I'd replace all three, and then once charged make sure charging volts are right. There are some crappy chargers out there (especially if old) that can ruin batts.

On mine, when first on charger it goes up to about 14.4 for an hour or so, then drops down to 13.3. If it stays above 14 long term, that is not good for batts.

Thanks for the replies. I have some investigating to do. Once I eliminate the inverter/charger as the cause, I'll probably replace all batteries with AGM. I've got 3 house, 2 start, and one gen battery - all LA. For now I've replaced the cooked one and checked both the others with hydometer and they were excellent. The hot boil probably took care of any sulfation if there was any. I'm going to discharge about 50% and then recharge while taking voltage, current, and temperature measurements.

If your starts are 8D I would wait until you need to replace them before going AGM. They are very expensive ($700-800) and VERY heavy. I mean VERY VERY heavy (160-170 pounds heavy)!

Inexpensive DVM are available that could be wired semi permanently so you can check at a glance what the charger & batteries are doing. Blue Seas offers them as do offerings from Amazon.
Use long enough leads that the meter can be brought up to the dash. Doesn't need to be pretty or permanent.
Once you are satisfied about which way you are going then wire the meter in permanently and neatly.

menzies said:

Consider replacing with AGMs.

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Sounds like your watering system failed you too.

I went away from 8Ds years ago. Couldn't handle the weight and paralleled group 31's get you the same capacity in the same space. Group 31 deep cycle LAs are hard to beat price per amp-hr. Thought I had the maintenance handled with the watering system, but thinking OldDan is right. Also this was the first time I learned that a dead cell or compromised battery could have such catastrophic consequences. I'm still thinking a temperature alarm is not a bad thing and pretty easy to do.

I had similar issue few years ago however, I replaced the failed batteries and the charger to ProMariner "Pronautic" that has a built is temperature sensor.
good luck,
see Manual;
View attachment 63110_use_precec.pdf

If you replace with AGM's, make sure the rest of your system can accommodate the new batteries' charging profile. If you charge them while under way, that must also be addressed. The charging profile for AGM's is different than flooded, and AGM's aren't particularly forgiving when it comes to charging. Even if your charger has an "AGM" preset, it may not be correct for the AGM you buy. Check the manufacturer's spec on charge voltages and insure that they're being met. Those details aren't insignificant.

I'd also add temp compensation, particularly if your bank is in the engine room. High temps can create significant overcharging issues since the higher temps lower the charging voltage profile. That could be what lead to the problems you're now attempting to clean up after. Changing to AGM's may not be a panacea, in fact it could create worse problems if the original issue isn't resolved. The battery overheating is likely just a symptom of a related problem that could be overlooked. Like- maybe the batteries are in the engine room and they're getting hot from the heat of the engine room, and your alternator is self-regulating, cranking out 14.4V when the batteries are already fully charged, and at 120F they only want a float voltage of 13.1 so they're boiling off the electrolyte and getting hotter yet....

The 12V system is just that- a system. Focus on a single part of that system at the peril of the whole. The devil's in the details.

All batts get warm while being charged.

There is need for a spacers so the middle batt of 3 can cool.

Sometimes hard to fit when stuffing 3 in an old 8D space.

I would see an event like that as both a sign and an opportunity to renovate my entire electrical system.

I think FF is on to something. The batteries are side by side - probably touching. I may be able to get a little gap between them. They are in the engine room. I live in south Florida so engine room temperatures are high in the summer - probably 110 when running and 120 at rest. This event happened the other day and temps were much lower, but I guess damage could have occurred to that battery over time. I did a hydrometer check about 6 months ago and all was well. As far as my electrical system, It's been a work in progress over the last 20 years and for my needs, I think I'm where I should be. Twin 90 amp alternators - one to start batteries (2 group 31 start/deepcycle LA), the other to house batteries (3 group 31 deep cycle LA). Both tied together with an ACR. A separate group 31 deep cycle for the generator. The house batteries are charged by the inverter charger that's rated for 30 amps, but measured at 60. The start and gen batteries are charged by a seperate 20 amp promariner charger. I usually leave the promariner off. At anchor I run a refrigerator and freezer that combined take about 7 amp hrs that may get used about 10 hrs on rare occasions as I usually run the generator. The cables are all oversized for the length of runs. From everything I've read - I do not need an external regulator for the alternators - my duty cycle just doesn't warrant that from everything I've read. Most of what I've read indicate that the external regulator applications work for under charging situations. The Lease-Neville internal regulators cut off before fully charged if anything, but I'm usually either running or on the generator.

Tbill- so you replaced the bad batt and the other two seem to be ok.

Definitely do this: let batts soak on whatever the normal charge source is, and check batt terminal volts with a decent meter. Let us know the voltage.

You might also consider adding batteries to your house bank. I have no clue what kind of boat you have or what kind of house loads you have. But asking 3 GRP31s to power relatively large house loads puts stress on the batteries over time and they will not last. That or combine your start batteries into your house bank and have a house/start bank using your isolated generator battery for redundancy. I know some people don't like to do this but I have done it on many different boats and it simplifies the system, has enough redundancy, and does not torture your skimpy house bank with excessive cycling. Also I have no clue what kind of reputation that brand of battery has, but just because it says "deep cycle" does not mean it is so. With batteries, you generally get what you pay for....and those batteries are cheap.

Someone also mentioned chargers. Like batteries, not all chargers are equal. There are some really good ones out there and they are getting better. If you are going to go through replacing batteries, especially battery types(ie AGM) you might consider getting a decent charger. I good charger matched up with good batteries will give you MANY years of trouble free operation. Not just 4-5 years, I am talking 7-10 years. Good luck and don't cheap out. You get what you pay for.

Ski - I'll get the voltage and post later.
Baker - The exide nautilus batteries are inexpensive, but for the life of me I can't find data driven comparisons of batteries. The best thing I've found is that the heaviest battery is usually the best. The Nautilus comes in the middle of the group and some comparisons say they are pretty decent batteries. I really don't have room for more house batteries and from all my reading 300 Amp-hrs should be enough for my needs. I will occasionally go all night without the generator and a very conservative estimate of amp-hrs (it's probably less) would be 100 amp-hrs. That is over a 10 hr period. Most of the time I'm running the generator due to need of AC in south FL. Also, my acr does combine the starts with the house until the house drops below 12.5 v, might be 12.4, so there is another 200 or so to draw from. I'm still not convinced AGMs are any better except for maintenance, and I'm aware of the different charging requirements. The AGMs seam to require a more delicate charging profile, which means I probably need to add an external regulator to my alternators if I go that way. My charger and inverter have AGM profiles built in and can be switched easily.

As far as cheap and neglected, my little boat has some no-name group 24 going on 4 years that is never charged accept by the 50 hp outboard. Not much load from the GPS/Sonar, but sits on the lift for months at a time and starts every time. Go figure.

Tbill36
Just an FYI and not trying to hard sell but I switched my 3 8Ds to AGMs for start/house & thruster banks in 2014 and have had no issues with stock Yanmar Alt.
I did change the shore charger profile to AGM but thats all. I am frequently back at home dock most nites or marina at least once / wk when on extended cruise. Otherwise gen charging AM & PM at anchor and Alt when underway.
They are still doing well and my plan at this point is to replace each 8D w a pair of GP31 AGMs when they shown signs of weakness.
I'm a fan of and use East Penn / Sams Club Duracells so the cost IMO is reasonable and a lot less than many of the premium ones out there and often touted as "better".

You should really have temperature compensation on the charger, especially with closely packed batteries. As the temp goes up, the charge voltage should come down. Even more important wit AGM.

TBill36 said:

I think FF is on to something. The batteries are side by side - probably touching. I may be able to get a little gap between them. They are in the engine room. I live in south Florida so engine room temperatures are high in the summer - probably 110 when running and 120 at rest. This event happened the other day and temps were much lower, but I guess damage could have occurred to that battery over time. I did a hydrometer check about 6 months ago and all was well. As far as my electrical system, It's been a work in progress over the last 20 years and for my needs, I think I'm where I should be. Twin 90 amp alternators - one to start batteries (2 group 31 start/deepcycle LA), the other to house batteries (3 group 31 deep cycle LA). Both tied together with an ACR. A separate group 31 deep cycle for the generator. The house batteries are charged by the inverter charger that's rated for 30 amps, but measured at 60. The start and gen batteries are charged by a seperate 20 amp promariner charger. I usually leave the promariner off. At anchor I run a refrigerator and freezer that combined take about 7 amp hrs that may get used about 10 hrs on rare occasions as I usually run the generator. The cables are all oversized for the length of runs. From everything I've read - I do not need an external regulator for the alternators - my duty cycle just doesn't warrant that from everything I've read. Most of what I've read indicate that the external regulator applications work for under charging situations. The Lease-Neville internal regulators cut off before fully charged if anything, but I'm usually either running or on the generator.

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If your charger does not have a temp sensor connected to one of the batteries that could easily be root the cause of the problem. The hotter a LA battery is, the lower the charge voltage should be. Charging a warm battery at too high a voltage can kill it quickly. Assuming your main charger CAN use a temp sensor and that the charger is actually still good, you may want to investigate adding one. Usually they simply plug in and the other end attaches to a battery.



Ken

Ski and others. I took voltage, amperage, and hydrometer measurements yesterday and today. The data is in the attached pdf. Basically took measurements as the boat sat for a few days with charger hooked up and all settled out. Then I shut off the charger, and disconnected the batteries from each other let it sit overnight. Hooked it back up, loaded it a little, recharged it and took the attached measurements along the way. The dates on the V columns are when the batteries were installed - the new one is 1/31/2021. I think the pdf is self explanatory, but please respond with any questions or observations.

TBill36 said:

Ski and others. I took voltage, amperage, and hydrometer measurements yesterday and today. The data is in the attached pdf. Basically took measurements as the boat sat for a few days with charger hooked up and all settled out. Then I shut off the charger, and disconnected the batteries from each other let it sit overnight. Hooked it back up, loaded it a little, recharged it and took the attached measurements along the way. The dates on the V columns are when the batteries were installed - the new one is 1/31/2021. I think the pdf is self explanatory, but please respond with any questions or observations.

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Charge voltage looks a kinda high unless they batteries were really cold, but I don't see anything weird other than that. What was their temperature at the time?

I hope this isn't a hijack because it was being discussed here. I won't be replacing my bank until 2022 but I'm planning to switch to AGM. I didn't think about the alternators. Do I need to put an external regulator in front of them? If so, can I just choose any of them, or are they specific to certain alternators / output.

Thanks
BD

DDW - temperatures were cold for us last night. Probabyl 40 deg which means my batteries may have gotten into the mid 50s. What surprised me was 12.9 volts after sitting all night and then having 6 amp-hrs removed. Most of the charts I've seen says 12.7 - 12.8 for fully charged batteries.

BD, you need to do a bit more research on this issue. First of all, you cannot just install external regulators without first altering your internally regulated units. Pretty much you will need to purchase new alternators. I strongly suggest that you take some time and read the excellent articles on this very subject on the marinehowto website.

If you do so, you will learn that, without adequately-sized externally regulated alternators, you will murder those nice new AGMs in short order. The charge acceptance rate for AGMs (40% of bank size) is indeed much higher than lead acid batteries which accept about 20%. That means that if you have a 1,000 amp-hour bank, you would need 400 amps of alternator to take advantage of the AGMs ability to take a faster charge. Even a lead acid bank would require 200 amps. Without a dual-belt or serpentine belt setup, you are limited to about 100 amp alternators on each engine. Even at that, withoutput sometimes throttled by the regulator because of high alternator temp, you won't get to 100 amps.

I think I have this about right but I am no expert. You will find the articles on marinehowto quite enlightening. One of them addresses the issues with AGMs specifically and, in particular, why and how AGMs are murdered. You may conclude, as I did, that AGMs, do not suit your boat.

BDofMSP said:

I hope this isn't a hijack because it was being discussed here. I won't be replacing my bank until 2022 but I'm planning to switch to AGM. I didn't think about the alternators. Do I need to put an external regulator in front of them? If so, can I just choose any of them, or are they specific to certain alternators / output.

Thanks
BD

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DavidM said:

Well, when the middle battery went dry it was probably a result lead sulfate accumulating in the bottom which shorted the plates. Shorted plates is what makes a battery run hot. If the other batteries are running hot too they are probably shot as well.

Replace all of the batteries and pay better attention to electrolyte level. FWIW while living aboard full time I only had to add water 3-4 times a year to my golf cart batteries. With good batteries and a good charger, batteries don't use that much water.

David

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Amen!

And, NEVER let wet cell batts get to or below 50% charge. Somewhat similar to keeping reserve fuel to accomplish a trip... I base my wet cell batt bank's need for recharge at 60% of remaining charge. That extra 10% of kept charge before recharging makes our wet cell batts last years longer.

Some of us, at least I, do not care about squeezing a year or two longer of battery life. So, more than occasionally, but not often, I discharge below 50%. My batteries are four years old and are still in quite good shape. So, I say to new boaters on this forum who are trying to make informed decisions, do not be afraid of the 50% boogeyman. Your batteries are not going to suffer catastrophe if they are occasionally depleted below 50% nor will their useful be affected in any measurable way.

Art said:

Amen!

And, NEVER let wet cell batts get to or below 50% charge. Somewhat similar to keeping reserve fuel to accomplish a trip... I base my wet cell batt bank's need for recharge at 60% of remaining charge. That extra 10% of kept charge before recharging makes our wet cell batts last years longer.

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catalinajack said:

Some of us, at least I, do not care about squeezing a year or two longer of battery life. So, more than occasionally, but not often, I discharge below 50%. My batteries are four years old and are still in quite good shape. So, I say to new boaters on this forum who are trying to make informed decisions, do not be afraid of the 50% boogeyman. Your batteries are not going to suffer catastrophe if they are occasionally depleted below 50% nor will their useful be affected in any measurable way.

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Safety is as safety does! Each to their own!! Ya just never know!!! and all the other soliloquies ...

In my experience: A deep cell wet, LA batt, when its charge is brought below 50%, faster sends and piles up debris on the bottom of batt container [even when fluid level is full]. Eventually that buildup can create a short between cells. Therefore raising batt temp and reducing batt usefulness... such as happened in one of the posts above.