INSPIRON 15Z battery charging light blinks 4 times orange

The charging light blinks 4 times orange and once white. I cannot boot or use the laptop with the battery, but only with the cable.

The battery icon in the bottom right corner says it's 100% charged.

"Start > Control Panel > Hardware and Sound > Power Options > Dell Battery Meter" says my battery is performing properly (obviously not true).

I ran the system diagnostics. The battery is detected, there is power (95% to 96%), but the "battery charging state" is "idle".

Please help. Thanks!