One Amp-Hour moves a certain number of electrons through the cell. (I forget the number as its been decades since I took those courses, but its a lot.) Each electron through modifies the metal in the cell at a subatomic level. After enough of this going on, there is not enough of those metals remaining to do any good. The manufacturer puts enough metal plates in the cell so that typically 10,000 Amp-Hours can be handled, to produce a specified amuont of Chlorine gas for a pool of a specified size. If the cell is rated for a larger pool, it will have more plates in it, or they will be thicker, or both. The 10,000 hours number seems to be a standard, but a manufacurer could choose something else. And it is really only approximate.
One Amp-Hour is one Amp for one Hour. I notice that my cell actually draws 7 Amps when it is running, so one Hour of elapsed operation actually uses up 7 hours of cell life, but on the other hand I only need to run it at about 8% power because it has so many plates. Your milage may vary. The Amps your cell uses is typically available from one of the diagnostic displays on the control box.
10,000 hours is just over 1 year, if you ran the cell constantly at 1.0 Amps. But you dont do that. Most cells run at 4 Amps or more so that 10,000 hours is really quite a bit less than a year. But when the SWG is turned off by a timer, that doesn't count. If you run it at only 25% power, then it is really only running 25% of the time so it lasts 4 times longer.
If you buy a cell that is rated for a bigger pool than you have, you do not need to run it for as long each day, or at as high a power, so it lasts longer. Usually the difference in price to get a higher rated cell is less then the life extension you get, so the usual advice is get the bigest one you can.
