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Post by mikesimonelli on Jun 12, 2022 17:42:54 GMT -6
2021 merc 250 17 hours on it. Yesterday I took a long night cruise only thing that’s on different from day time is 4 led lights that have been on the boat for years. Agm batteries are 4 years old. So I got back to slip go to open battery lid and the electronics battery is burning hot. Everything still working fine. Took battery out just incase something happened let cool over night. Put back in next day took a cruise. Battery switch is on both and after an hour battery is starting to get hot. Just the one not the starting bat.
Everything still working and smart guages read 14.4-14.6 while driving. Is it shot if they were over charging both would get hot right? Is it overworking? Nothing has been added same setup except new motor end of last season.
Is it on its way out? I had everything on today jwhen I went out I was checking every 10 min it was warm about 20 min i to ride didn’t start to get hot until an hour in and it get pretty hot. Starting bat is cold as ice.
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Post by Juan on Jun 13, 2022 3:40:55 GMT -6
Sounds like a shorted cell. You can check by disconnecting the battery, try to charge it, then let it sit for a few hours and usi g a voltmeter, check the voltage. If under 11 volts, the battery is bad. A fully charged good battery should read between 12 and 13.8 volts.
Edit: Forgot to mention...before doing anything else, check the wiring at he battery for heat.. it's possible the short is in the wires connected to the battery and not a battery cell but I'm betting it's one or the other and probably a cell since the wires would probably melt or burn if shorted.
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Post by mikesimonelli on Jun 13, 2022 5:56:57 GMT -6
The batteries have been wired the same way since they were put in 4 years ago. Today battery read 12.9 started went to 14.5 and everything works fine. Didn’t have much time so only let idel 30 min house bat got warm start battery ice cold.
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Post by Juan on Jun 13, 2022 6:36:45 GMT -6
When you start it, you're reading the alternator voltage which is always higher than the battery voltage. It's possible something you have connected to the battery went bad and shorted but if you're sure none of the existing wires are getting hot the problem is probably an internal short in the battery. It can happen when sulfer builds within the battery after time. You might try swapping your house and start batteries. If the house battery still gets hot it's time to replace it.
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Post by mikesimonelli on Jun 16, 2022 12:29:43 GMT -6
So today I put both batteries on the charger at work. After an hour one was red hot one was cold. So I’m guessing it’s the battery.
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Post by Juan on Jun 16, 2022 16:04:32 GMT -6
Yep. Time for a new one. Not recommended and it's not a permanent fix but I've seen shorted batteries unshorted by dropping it hard. That can break loose the sulfur that has the battery plates shorted inside the battery.. Don't try it with a lead acid battery before draining the acid but it won't hurt to try it with a sealed AGM.
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