The average lifting capacity of stairlifts is 300 pounds; some are capable of hauling more than that. The load capacity notwithstanding, stairlifts need a power source to keep them running to and from, or rather, up and down the stairs with their fares. We like to think of stairlifts as steamboats that need coal to keep the steam puffing. With stairlift the case is a different, they need a better, cleaner source of energy, hence electric current, either direct or alternating.
Stairlifts Driven By Alternating Current
AC is a clean source of energy and the cheaper of the two. AC devices and all the gadgets that come into play. AC power units are placed in a loop under the seat which can un-loop and reloop as the chair ascends or descends down the rail. These are also fairly easy to maintain because, no one needs to open up the entire chassis to replace a battery or make a simple repair. For their low price and simplicity, AC power units are mostly used all around the globe.
The biggest downside of having alternate power source seems to be ever dependent on the grid supply. Latest products have found a way to circumvent this issue by cleverly installing a direct current backup source as a fallback measure, allowing the lift to keep operating for a while or at least complete its ascent or descent.
Stairlifts Operated By Direct Current
As already mentioned, AC units will not and cannot run long after power grid has failed. Even those fall back battery packs are not capable of running more than a few times before dying out. To make sure that you get more out of the energy source and keep the unit running even after power has failed, you will have to invest some more and buy a battery operated rig. These units are in fact AC units with a very large battery. The battery and the conversion unit that changes AC into DC and stores it in the battery is what make these costlier.
Though these will cost you more than your average power sources, but these will certainly be better. Finally, if you stay in an area where electricity supply is steady then you need not invest a lot in DC units for your stairlifts.