The battery is no longer good to use in the tablet. Discard the battery according to the environmental laws in your state, don't throw it in the garbage. There are places that take these and recycle them safely.
You can buy a new battery here if they are still in production for your tablet model:
You can also remove the battery and work without it, but get a 150-200 VA battery backup power supply for about the same price. Plug only the AC-adapter in this device. This will keep the tablet running, just like the internal battery, in case of a power outage while the iQ is running.