I can't say I've ever needed a maintenance contract for a defib and have, over the years, looked after several. Someone needs to keep an eye on the equipment to make sure it's operating properly (in all of ours there's a simple green light, easily visible) and periodically (over several years) make sure the pads and battery are up to date. Pads last at least a couple of years and I've only had to replace a battery one and it was a very simple procedure to order a new one and fit it. If you register the equipment with The Circuit, they'll remind you when things might need replacing. Otherwise, no maintenance required.