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Discussion Starter #1
Hi,

When I came on board my C30 the other day, I realized my batteries were boiling. I shut of my battery charger and sake of good order also disconnected my shore power. I was puzzled as to why they were boiling as I hadn't been on board for a few days and I would have thought that the batteries were fully charged. What puzzled me even more was 10 min. after disconnecting all power the batteries were still boiling.

I have 2 Flooded Lead Acid Deep Cycle 75 AmH which are being charged by an OLD Pro Mariner 30 battery charger (I have a photo of the charger, but can't seem to upload).

I am thinking that my battery charger is over charging the batteries, but I would be very pleased to hear your input on my situation.

Thanks!

//Frigast
 

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Yes likely but in general

never trust charge sources' sensors and displays, always monitor, regularly check their accuracy

measure volts and amps at the bank

with independent known good tools

never allow a charger to equalize / condition automatically, should only be done manually.

Boiling is a completely normal part of the later stages of properly adjusted FLA charging, but only within the above contexts, and

that does sound dangerously extreme, and you may have just prevented a serious fire if you hadn't been there
 

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When you say "boiling", do you mean:

* Making a bubbling sound
* Really hot

The first one isn't technically "boiling", it's a chemical reaction that's pretty normal during charging. It's why you have to check the battery fluid levels frequently. However, the amount of bubbling goes up the more aggressively the batteries are being charged, so it still might be an indication that something is amiss.

If they're getting really hot, that's usually a bad sign.

The charger might be fried and stuck in bulk mode or something. Need to get something like this to find out what it's really doing: https://www.amazon.com/AstroAI-Multimeter-Resistance-Continuity-Frequency/dp/B07MT8N8BM/ref=sr_1_8?crid=16IP9PFNJ8ZFI&keywords=clamp+volt+meter&qid=1560548359&s=gateway&smid=A5IGHX1C7KI5E&sprefix=clamp+volt,aps,164&sr=8-8
 

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For permanent use a shunt + separate display type is very cheap these days.

Can even be used in portable mode with a collection of strategically placed Anderson junctions
 

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Discussion Starter #7
Many thanks for all the replies!

With regards the the Multimeter, how 'big' should I be looking for? I would assume that meters maxing out at 400A would suffice, but please correct me if I should opt from something slightly larger.

I've read a little bit more regarding my battery charger and there seems to be quite a few horror stories due to heat generated from overcharging. Therefore I've decided to update to a modern smart charger. Presently, I am considering the ProNautic 1220P.

With regards to a shunt and permanent display, one of my future projects is installing a battery monitor.
 

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400A should suffice for a multitester.

As far as chargers you should have a charger that puts out 10% of your battery banks capacity. Also factor in the draw your boats systems take so if you have a fridge or lights in the boat at night you might want to up your charger size. Bigger is generally better. Here is some info on chargers. Also follow the link to his web store and find good prices on Sterling Chargers.
https://marinehowto.com/installing-a-marine-battery-charger/

First thing you should do is buy a multi meter and make sure you are not fixing something that is not broken.
 

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If going to AGM (not advised unless necessary) then much higher C-rates, and closely adjusted charger setpoints are called for.

Great thing about FLA (out of many) is you can't really overcharge them, long as you keep the water level up.
 

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Ammeters with higher current range capacity will often have poor accuracy in the low ranges.

Unless you need to accommodate measuring very high amp loads, expensive gear capable of capturing high startup transients,

you can save money by just covering the highest rates you ever plan to charge at.

For a tiny bank like that you want decent accuracy below 1A for setting the charge termination endpoint
 
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