12v Deep Cycle Gel Battery - minimum voltage under load

[Ian]

I've got a 100aH 12v deep cycle gel battery (OUTDO/HUAWEI OT100-12 GEL 100Ah 12V) which I'm using on a portable cart to power an inverter and a few 12v accessories.

It's running well and I tried a few larger (1000W) loads on it today, to give it a bit of a stress test. I'm using a shunt for accurate voltage measurements while under load.

I noticed that with high loads the voltage can drop to 11.7v. Can anyone advise if this will harm the battery and what the low-voltage cut-off should be? I've seen 11.5V mentioned on a few forums, but not with any great detail. I appreciate that under no load, I shouldn't let a gel battery drop below 12.1v without causing damage. It's not the cables causing the voltage drop, as I'm using short runs of 35mm² cable - plenty for this load.

 

[piglet11]

A voltage drop is entirely expected. If you put a voltmeter on a car battery while turning the engine over, it could go very low.

What does the damage is long spells at a partially discharged state, say 10.5-Volts. A short surge shouldn't damage it subject to things like cables and the internal resistance of the battery. Below 10.5-V for long, you might not be able to recover it.

I would have a close look at the datasheet for that battery and see what it has to say about charging and discharging. For information, the charging voltage for a standard 12-V lead acid battery is 13.78-volts, but that quickly falls once off charge.

100-Ahr is a sizeable battery and expensive to replace.

 

[CACJL]

Discharging a battery at the one hour rate (100 amps) for any length of time is not good, see the manufacturer's data sheet.
I agree with piglet11, the oncharge voltage should exceed 13.8 volts, otherwise the battery will start producing Hydrogen to the detriment of the electrolyte.

 

[Ian]

Thank you both, I'm going to limit the discharge to ~25A while I'm just using the single battery. I spoke to the very helpful supplier and got the following graph which helped a lot: