Current will only flow when a load is connected. If you confirm it is really broken, then you should look for the two big parts (transformer and rectifier). Unfortunately, the fact that it is able to output 12 volts means both are working and some control circuitry is then messed up.
Can a faulty battery charger meter show a current flow?
A faulty battery charger Amp meter may not display any current flow in your battery. If you use a defective charger amp meter, you have to replace or repair it from your nearest auto shop. So, check the charge level in your battery and look at the Ammeter for any faults. Why is your battery charger clicking on and off?
If the battery and battery charger's connection is loose, the battery charger clicks on and off, which might be why you're having trouble reading the AMP meter. Here's how to read a battery charger amp meter and a digital Ammeter: check for a loose connection between the battery and charger.
A battery charger's AMP meter can become defective. If you notice the Amp meter is not functioning correctly, take steps to fix it as soon as possible. Fixing a battery charger's Amp meter will not cost you heavily. A multimeter, which is required for the repair, is not expensive.
To use a battery charger AMP meter, first, select the battery charger amp. Then, turn on the amp meter and let it do its job. You will see the amp meter indicator or needle going to your determined point slowly (2 amp or 10 amp). During the battery charging process, the amp meter will go down slowly.
If your battery charger needle is not moving at all and is staying at the same point, it could be due to a faulty battery charger Amp meter that can't show you the accurate, current flow in your battery. Another possibility is that your battery charge is too low.
When you first connect and switch on the charger, the needle will move sharply to the right. After a few seconds, you will see the needle gradually move to the left. It will settle at a steady charging point, showing the amps flowing. This is a good sign that the charger is working. How To Tell When A Battery Is Fully Charged On A Battery Charger?