They are hardwired, to stay on trickle charge. And they need to be serviced once a year (check battery, check that the pads are not expired). So your best bet i

They are hardwired, to stay on trickle charge. And they need to be serviced once a year (check battery, check that the pads are not expired). So your best bet is to call the phone number on your fire extinguisher, which also needs yearly inspections.