Why is my laptop dying quickly after disconnecting from power?

See if you can obtain a replacement battery.

Third-party replacement batteries can be dangerous if manufactured improperly or if there are wiring/component-related issues from poor component choice. Make sure that you're actually getting an OEM part (many vendors will list their parts as OEM when in fact they aren't) or one that is considered safe (such as from iFixit). Poorly designed battery packs can catch on fire, leak or even explode, causing personal damage and/or injury.