How to fix inverter/charger not charging batteries

Is your inverter/charger failing to charge your battery bank?

While each inverter/charger may be different and indeed you should consult your inverter/charger manual first, I have listed below a summary of common causes of inverters/chargers failing to charge batteries and how you can fix them.

Note: These tips assume you are comfortable working with electricity. If you are not, consult a certified technician or your inverter’s manufacturer’s technical support for assistance.

Note: This post refers to inverter/chargers, i.e. a combined inverter and charger into one unit.

Common causes of an inverter/charger not charging

First the symptoms of an inverter/charger not charging

When an inverter charger fails to charge a battery bank, you will likely have:

AC power/ shore power/ generator power on
Batteries are flat – which should not be the case if the inverter/charger is working
Appliances connected to the inverter fail to work

Lets go through a list of fixes you can try.

What to check if an inverter/charger is not charging

# 1. Confirm that there is power supply to the inverter/charger

Confirm that the inverter/charger is received shore power/ grid power or generator power

Check that the circuit breaker on the 120V line to the inverter/charger is ON and not tripped

If your inverter/charger has an inline fuse or resettable breaker on the inverter itself, confirm that the fuse wire is still intact (has not blown). Consult your inverter manual for the location of the inline fuse.

Note: Anytime you have a blown fuse, faulty breaker, try to investigate the cause before resetting or replacing the fuse. Perhaps it is as a result of a short-circuit.

Loosely connected battery cables

If there is no short-circuit or the fault that caused the blown fuse has been cleared, you may then proceed to reset or replace the blown out fuse. If unsure, consult a trained professional!

# 2. Check the connections from the battery to the inverter/charger

Make sure that the inverter charger cables firmly hold the battery terminals. The inverter/charger WILL FAIL to charge the battery if the cables do not make good solid contact with the battery terminals.

This may be because they are not tightly fastened, are rusty or have the bluish green copper oxide residue and need to be cleaned.

Extremely low battery voltage

The inverter/charger voltage needs to be above a minimum threshold ~11.5V for a 12 volt inverter for the internal electronics of the charger to activate so that charging can begin.

Should the battery voltage be extremely low, the inverter/charger may fail to charge the battery. When this has happened to me in the past, I charge the batteries using solar panel directly so that the voltage picks up to about 11.5 V and then connect to inverter/charger.

# 3. Your batteries may be dead or need service

If your batteries are dead or failing or are not serviced, they can fail to pick up charge and even when they do, on connecting appliances to the inverter, the battery voltage drops fairly quickly.

First, check your battery service history. For the flooded lead acid batteries, check that they have been topped up with distilled water to the recommended level.

Next check – what is the expected life time of your batteries? How old are your batteries? If your batteries are about or past the expected life span, then you may have a case of failing batteries.

If the above checks out alright, then you most likely have a faulty inverter/charger. Consult your inverter/charger manufacturer’s technical support.

Hopefully, your inverter/charger is still under warranty. If it is not, try to get an indication of the likely repair costs compared to the replacement costs to see which is the better option.