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Author Topic:   Battery Becomes Very Hot in Normal Operation
best posted 06-07-2006 12:04 AM ET (US)   Profile for best   Send Email to best  
I just put in my Boston Whaler boat, and I ran it 14 miles to its dock. While I was checking out and cleanning the boat I happened luckily to notice that one of the two batteries was really hot. I disconnected the battery and removed it from the boat. What caused this heating? The boat has twin engines and two battery switches. I ran the boat the battery switches on ALL. I really thought that the battery was in danger of expoloding. Thanks for any input.
highanddry posted 06-07-2006 04:00 AM ET (US)     Profile for highanddry  Send Email to highanddry     
There are several possibilities including you have an internal short in the battery or there is a short in your wiring. Quite possibly in the Perko switch were all the wires run to, perhaps one has rubbed into another. I noted this possibility when I installed dual batteries and added extra wraps of insulation and varglass to prevent a short across the batteries or to ground.
Chuck Tribolet posted 06-07-2006 10:25 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Check the state of charge on the battery with a hydrometer.

If all the cells are down, you have a short in the wiring.
Find it, fix it, and be suspicious of the battery -- they
don't like being run dead flat.

If one cell is down, it's probably internally shorted and its
time for a new battery.

If all the cells are up, check the charging voltage on that

And check battery water levels in any event.


Bulldog posted 06-07-2006 04:33 PM ET (US)     Profile for Bulldog  Send Email to Bulldog     
Best , you stated that you have twin engines with two battery switches and you ran them both in "all". This would tie the two batteries, and the two alternators on the engines together, this can be a problem with the charging circuits. You should try and keep the systems isolated from each other unless you are in a low battery situation then tie the systems together for a short time. Chuck is right on, with how to check the battery, and I hope it is a bad battery, the charging circuit on a motor isn't cheap. Have you always run you boat with the switch in the "all" postion?....Jack
best posted 06-07-2006 06:52 PM ET (US)     Profile for best  Send Email to best     
Thanks for the input every-one. Jack, I normally run each engine on their own battery, not together...I picked the boat up from the marina and assumed they would not have had the swithches on all...I am going to replace the battery, run the switches separatly and hope the regulator did not blow out or their is no short. Thank you for you're ideas.
minitauk85 posted 06-07-2006 07:39 PM ET (US)     Profile for minitauk85  Send Email to minitauk85     
What type/year motors are you running?-k
jimh posted 06-07-2006 08:19 PM ET (US)     Profile for jimh  Send Email to jimh     
There are two possible causes for the excessive heat:

--an exothermic chemical reaction
--flow of electrical current through a load which produces heat

Chuck Tribolet posted 06-07-2006 09:17 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
And the "load" can be very small if the current is high.
A lead-acid battery can source well over a thousand amps
briefly. At 12V that woud be over 12000 watts. The
resistance of the lead plates, small as it may be, will
make them get hot. And I suspect there's some resistance
across the acid too.


rtk posted 06-07-2006 11:30 PM ET (US)     Profile for rtk  Send Email to rtk     
Do you have a volt gauge for each engine? What were the readings while running if you do?

Not clear on the battery set up. Twins, two dual battery switches and four batteries?

Low voltage readings (less than 14.2 or so) generally indicates a charging problem or an excessive load (short of some kind).

Voltage readings well in excess of the engine charging specifications typically indicate a problem with the charging system. Batteries can be "overcharged" and will heat up if they are.

I like to start my troubleshooting with a voltage reading on each battery while the engine is running. If there is a voltage difference when switching batteries, a battery is the likely problem. If charging voltage is not right when running off either battery it is likely a charging or wiring problem.

I actually pay more attention to my volt meter on my boat than water pressure or temperature readings. If voltage reading are steady and in spec, I am confident that all is well with regard to the electrical system.


jimh posted 06-08-2006 09:18 PM ET (US)     Profile for jimh  Send Email to jimh     
To any chemists reading this discussion: is the process of charging a lead-acid battery exothermic or endothermic?

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