This was installed for my partners use, before she passed away. Now, whilst it has no use, I am reluctant to remove it, but....
I was wrongly informed by the installer, that the large switch on the rear of the bit you sit on, isolates the battery. In fact it doesn't, because the battery inside it still goes flat if it is left without mains power for any length of time.
I cannot see an obvious way to get inside, to disconnect the battery. It seems silly to have it permanently on charge, so switching it off and isolating the battery seems the sensible way to go.