Hard to tell from the pictures, it doesn't look like the battery has a balance plug. If it's a single cell battery, that's OK.
Two possibilities, first, the battery has more than 1 cell & you have the charger on a balance mode. You can't use a balance mode on the charger without a balance plug.
Second, the battery is not making an electrical connection. It looks like a servo plug, which if plugged in backwards would not be making an electrical connection. It could also be the pins inside the connector, the pins may not be connecting. I have had issues connecting balance plugs, one pin not connecting & throws the whole system off.
These types of problems are difficult to solve. Just chase the problem one connection at a time.