Thread: Deep cycle batteries and dual batt systems.

Hi loanrangie, leave the battery to settle today, then give it another charge over night.

Tomorrow, apply a small load of around 3 to 5 amps for an hour and measure the voltage. This is roughly a 5% load on a 100Ah battery.

A fully charged battery, able to hold it’s charge and with the load still connected, should have a voltage reading of no less than 12.5v after an hour of discharging with that small load.

If the battery is stuffed, the voltage will quickly drop to 12.3v or lower.

This would indicate the battery is no long able to hold a charge and time to replace it.

With the load attached, the chart below will give you an idea of what you should be seeing.

I have used a couple of ex UPS batteries with various degrees of success. A couple of points:

As you said the battery may have been on its last legs, some UPS applications will turn off the load when the power goes out, many will just run till they're flat hoping the power comes back, this will cause them to degrade, thus scheduled replacements.

I've been told as the batteries are designed for fixed installation, the vibration in a 4WD can kill them, this might have contributed to the failure also.

I'm using another repurposed battery at the moment, the way I look at it, if it's free I'm not going to be heartbroken if it fails like I would an expensive high quality battery.