I have a cordless electric lawnmower that runs on sealed lead acid batteries. It is on it's second battery, which has noticeable degraded performance and will need replacing soon. My question is why the original battery, which was rated at 17 Amp-hours, lasted twice as long as this second battery that is rated at 22 Amp-hours. The two batteries are the same physical size, externally -- so it's not the case that the 22 A-hr battery is simply a "scaled up" larger version of the 17 A-hr design. Some other details... 17 A-hr battery: lasted 3 years, at which time I thought it had died, which turned out to be wrong. One of those years, I was mowing a friend's lawn as well as my own, so it's pretty reasonable to say this battery lasted the equivalent of 4 years and was still in working order. 22 A-hr battery: has lasted 2 years, and is noticeably degraded (as I mentioned earlier) Also, the two batteries are different brands, which might be an explanation for the different lifetimes. However I am wondering if there is some fundamental design difference that would allow a 22 A-hr battery to be the same size as a 17 A-hr one, but also would result in shortened lifetime. Mainly I am thinking about the size (area or thickness) of the electrodes, or the total number of electrodes per cell being different -- or something along those lines. Thanks in advance for any insights.