If your battery is in a poor condition you'll be wasting valuable power in an off-grid / renewable energy system as the battery won't be charging properly. In our series of hints and tips on ensuring you get maximum benefit from your batteries we take a look at charging batteries and how you can tell whether you have a healthy one.
The best way to check the health of your battery is to measure the voltage. Routine voltage checks will not only show the state of charge but also help spot signs of improper care such as undercharging and over-watering. For accurate voltage readings batteries must remain idle - so no charging no discharging - for at least 6 hrs preferably 24 hrs.
You'll know it is time to replace your battery if you fully charge the battery and then measure the voltage after the battery has had time to settle and the charge is less than 70%.
- Disconnect all loads from the batteries.
- Measure the voltage using a DC voltmeter.
- Check the state of charge against the voltage reading see table below.
Try not to let the battery discharge by more than 50% before it is charged again. In fact many experts recommend operating batteries only between the 50% to 85% of the full charge range. Discharging by more than 80% will damage (or even kill) the battery and it is inadvisable to leave batteries deeply discharged for any length of time.
State of charge as related to Open Circuit voltage
|Percentage of Charge