I have two CatGenies, both of which take a proprietary cartridge that are good for sixty cycles. The CatGenie will not run without a non-empty cartridge installed. In my home, each unit runs four times a day (I have six cats), so a cartridge lasts only fifteen days. Each cartridge is about fifteen bucks. For those of you following along without benefit of a calculator, that totals sixty bucks a month in cartridges.
Environmentally, four cartridges per month equals a lot of foil, plastic and little circuit boards in the landfill - and I really don't see how CatGenie could sell refills without totally redesigning the cartridge.
Adding new solution to an empty cartridge is not that complicated (see my other instructable), but it isn't really helpful because the cartridge has a microchip on it that acts as a counter. When the counter reaches zero, the cartridge is trash. This instructable will demonstrate how to reset the counter on the cartridge to "full" - allowing you to drop it back into the unit and rock on.
This instructable does cover resetting but does not cover refilling the solution in the cartridge; it assumes you have done so already. If you need help with the refilling process, please see my other instructable.