Check first your power supply if it still working.
* Remove connecting terminal of your battery and check the positive and negative terminal wires if there's still voltage output. I yes, may your battery was already damaged (Replace it). If no voltage output or has a lower voltage output, replace your power supply battery charger.
* If you want to use it without the battery anymore, you can use a power supply that has the same voltage/current rating to your charger/battery. Connect the power supply directly to the battery terminals after removing the battery.
I hope it can help.