Battery issues

[Landy7]

I had some troubles in the past with the alternator not charging the batteries (I have 2, one for winch and one for all the rest, both are separated by a charging splitter). I changed the regulator but the problem was the excite wire, that had bad connection. I fixed the excite wire and went on a big trip.

After a drive all day, I shut down the engine and hear a sissing sound from where the batteries are. The main battery was boiling.. How can this happen? I read online that car batteries boil when they are overcharged. How can they overcharge? By having a bad regulator? I swapped out the main battery and connected the winch battery (thank god for 2 batteries). I could drive home (3h) perfectly and upon arrival the battery was cold so I assume the regulator is fine?

Any tips on having a tool connected to the battery to continuously have information on charging levels etc? How can I know if a battery is overcharging? If it's charging it could read about 14v but how can you know when this needs to drop to for example 12.8v?

[Bowie69]

It is normally only a bad regulator that will over charge a battery, the hissing is indicative of that, however you say the other battery was fine? If so then I suspect you just had a battery go bad on you, perhaps shorted internally which caused the heat and then hissing.

As for a monitor, any of the really cheap things are fine, it is only measuring voltage after all, e.g. 12V-60V Car Motorcycle Marine Battery capacity indicator monitor Voltmeter Meter | eBay

[Landy7]

Thanks, the second battery is indeed fine, even after a 3 hour drive. I just checked the voltage on that battery, 12.8v in resting state (not been driving for a couple of days), so it appears all ok and maybe the first battery died on it's own and not due to the regulator. The regulator is a new one from Hitachi.

I will order a voltmeter that I can connect permanently but I still struggle with how I should interpret the readings. +/- 11v battery is empty. Below 12v battery is 50%. >12.6 battery is full. When charging, it will be between 13.5v and 14.8v, but how can you know when it's full and the regulator should stop charging the battery? Overcharging is when it's producing more then 15v? 

[FridgeFreezer]

1 hour ago, Landy7 said:

I will order a voltmeter that I can connect permanently but I still struggle with how I should interpret the readings. +/- 11v battery is empty. Below 12v battery is 50%. >12.6 battery is full. When charging, it will be between 13.5v and 14.8v, but how can you know when it's full and the regulator should stop charging the battery? Overcharging is when it's producing more then 15v? 

People get very hung up trying to interpret battery state from volts and the short answer is it's 50% impossible - a battery is a bucket of chemicals and measuring the voltage tells you about as much about what's going on inside it as measuring the temperature of a cake tells you about whether it's poisonous or not.

Battery voltage is a useful measure though - it certainly tells you if your battery is low (<12v) dead/very bad (<10v), charging (>13v), or being boiled to death by a faulty alternator (>15v).

While it's possible one battery "just died" it's also possible that your alternator is still faulty and the battery that died sacrificed itself, saving the other battery. I would look very carefully at what's going on because the alternative options to a boiled battery include a vehicle fire or a battery explosion and you don't really want that.

A £10 digital multimeter from ebay is a more than good enough diagnostic tool for an old Land Rover to keep in your toolbox.

[Landy7]

Thanks, I ordered a voltage meter that I can permanently connect to the battery to have a good eye on what's going one. Like you said, I want it to be safe, and the boiling battery incident was a bit of a scare, we all know where the batteries are installed in a Defender, we don't want them to blow up.. On the next drive, I will carefully look at all the readings I can get. 

[Snagger]

It’s worth checking the alternator output over a range of rpm to make sure it isn’t overcharging.  I think it’s also a good idea to make sure the battery compartment is well ventilated to the exterior to prevent toxic or flammable gas accumulation.

[Landy7]

Good idea about the rpm's, the day the battery boiled was an off-road day where I spent lot's of time in low range revving the engine on some steep climbs, over and over again.

Edited September 27, 2023 by Landy7