Generator battery exploded

Chiefsfan

Member
Feb 21, 2019
32
Gilbertsville Ky
Boat Info
1996 370 Sundancer Raymarine C120
Engines
7.4 Mercruiser v-drives
Yesterday evening I attempted to start my generator to let it run and get some stabilized fuel in the lines and carb. The second I hit the start button from inside the cabin at the panel, I hear a very loud bang that scared the &@€* out of me. Couldn't get up those stairs fast enough, open the main access hatch to see and smell acrid smoke and acid. The generator battery EXPLODED!! There were battery parts and acid everywhere. Took a couple of hours with a baking soda and distilled water solution to get it all cleaned up. My question is just how common is this? One piece of the battery top shows that it was a deep cycle battery, why wouldn't that battery have been a starting battery?
 
3 main causes of battery explosions are 1) over-charging, 2) insufficient water, or 3) hydrogen build up. My money is on #2 with #3 coming in a close second. It's doubtful that using a deep cycle as a starting battery had anything to do with it, particularly with the relatively small load required to start a generator.
 
That happened to me years ago with a boat I had just purchased. I believe the cause was low water with the plates exposed. Hydrogen in the battery and the exposed battery plates with bridging across the plates causing the spark. I now check the batteries often and warn friends to do the same.
 
3 main causes of battery explosions are 1) over-charging, 2) insufficient water, or 3) hydrogen build up. My money is on #2 with #3 coming in a close second. It's doubtful that using a deep cycle as a starting battery had anything to do with it, particularly with the relatively small load required to start a generator.

Agree with all three above. #2 causes #1 which causes #3 which results in BOOM! Boats left plugged in all winter can blow up and catch on fire. Most marinas do not allow boats to be left plugged in unless the owner is present for this reason.
 
I have never left a battery on a charger full time before owning a boat like this, and never even thought about the possibility of a battery exploding. I completely understand what you guys are telling me, and in hindsight it makes perfect sense. Those batteries are going to be checked very regularly from now on. I'm also going to turn off the charger.
As far as age of the battery, not enough of it left to piece together to tell. Charger looks original, so a '96 model.
Would the battery exploding cause any additional damage to the electrical system on the boat?
 
Agree with all three above. #2 causes #1 which causes #3 which results in BOOM! Boats left plugged in all winter can blow up and catch on fire. Most marinas do not allow boats to be left plugged in unless the owner is present for this reason.

I have never been in a marina that did not have boats connected to shore power without the owners present.
 
The battery exploding will not "harm" the electrical system. As long as you were able to clean up the mess and mitigate the acid you should be ok. One way to make sure you got rid of all the acid would be to use a baking soda mixture with warm water in a garden sprayer to wet down the surrounding area in the bilge and rinse with clean water.

BTW some will disagree but I don't get all exited about all the new "smart" chargers. My charger is the old style 34 year old ferro charger and I leave it on 24/7 while in the slip with no issues. The key is to keep the water level above the plates and get rid of bad batteries as they fail. Any charger will continue to send amps into the battery if the required voltage is not reached and cause potential explosive gases to result. I get 4-5 years out of my flooded wet cell batteries and check the water in the spring, mid summer and early fall. If you add water to a battery late fall and the water does not have a chance to mix in with the acid it can cause the battery to freeze. Once a battery freezes you may as cell toss it.
 
I have never been in a marina that did not have boats connected to shore power without the owners present.

My comment is meant to refer to boats stored on land during the winter not while in the water in season. Boats stored for the winter on land are usually packed together and left unattended for long periods and if they catch on fire the results are catastrophic.
 
Do AGM batteries have this issue? Definitely would not explode due to lack of water, they are not serviceable, but maybe if left connected to an older charger that never turns off? Anyway, get an AGM battery. No maintenance, no worries, and they can be charged up with any old charger, just don’t leave the charger on for long periods of time.
 
I have never left a battery on a charger full time before owning a boat like this, and never even thought about the possibility of a battery exploding. I completely understand what you guys are telling me, and in hindsight it makes perfect sense. Those batteries are going to be checked very regularly from now on. I'm also going to turn off the charger.
As far as age of the battery, not enough of it left to piece together to tell. Charger looks original, so a '96 model.
Would the battery exploding cause any additional damage to the electrical system on the boat?

First order of business, should be to update the onboard charger to current technology. The new "smart" chargers will taper off the charge when the batteries reach capacity. That being the case, you can leave it hooked into shore power 24/7. Doing so with an old dumb charger will sit there and cook your batteries which is more than likely what happened.
 
First order of business, should be to update the onboard charger to current technology. The new "smart" chargers will taper off the charge when the batteries reach capacity. That being the case, you can leave it hooked into shore power 24/7. Doing so with an old dumb charger will sit there and cook your batteries which is more than likely what happened.

I disagree with this statement about old "dumb" chargers. My 1986 390EC has the original ferro charger. I leave it on 24/7 all summer and it has never "cooked" a battery. On my last boat I had an expensive "smart" charger that did cook my batteries because I did not maintain the water level. Since then I pay close attention to the water level in my batteries. That was 15 years ago and never had a problem since with either new old type chargers. Don't let having a "smart" charger fool you into thinking you they will keep you safe.
 
Well I can tell you that this battery issue has been a relatively cheap learning experience, and a lesson was learned. Battery maintenance is now on the checklist...
 
Less volatility with agm batteries. Although you can never eliminate all risk. If you're using flooded, weekly fluid checks are advisable.
Microprocessor controlled chargers are far superior technology to ferroresonant units.
They can maintain the optimal charge curve and compensate for temperature variations.
Doesn't mean you don't have to do maintenance on flooded batteries but the charging profile is much more conducive to longer battery life. I switched to agm years ago. Never go back. They're cheap enough now to make it worth it.
 
As far as AGM batteries go, can you have a mixture of flooded and AGM in the battery bank. I guess what I'm asking is can I replace the old batteries one at a time as they start to go bad with new AGM batteries, or do I need to replace all four at the same time?
 
As far as AGM batteries go, can you have a mixture of flooded and AGM in the battery bank. I guess what I'm asking is can I replace the old batteries one at a time as they start to go bad with new AGM batteries, or do I need to replace all four at the same time?

Not good to mix chemistry. You may get away with it but not optimal. I would replace all at once for a consistent base line. Sams club has the best deal around for Duracell agm.
 
That's pretty much what I thought. Will the OEM charging system be compatible with the AGM batteries?
 
That's pretty much what I thought. Will the OEM charging system be compatible with the AGM batteries?

Maybe? Newer chargers can auto sense the type of battery. Older ones may have a battery type selector switch.
 
That's pretty much what I thought. Will the OEM charging system be compatible with the AGM batteries?

Compatible - yes. Optimal - probably not. The AGMs have a different charge profile. Longest life will be realized with a charger that has a profile specific to AGMs.
 

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