Its a useful discussion, if only to show the confusion about the LiFePO4 batteries. I've just got a Bienno 20AH battery to replace my old 20AH lead-acid battery (that really didn't give me a useful 20AH, as neither did the same lead-acid battery before that). 20AH is a large size for a glider, but I need a heavy nose battery for my motorglider anyway. The Bienno is a featherweight compared to the lead-acid, so I may need to add some weight in the nose now. I decided on a 20AH capacity because 1) it was the exact same size as my old lead-acid 20AH battery, so the battery holder didn't need to be altered 2) I distrust the manufacturer's claims of capacity, so only expect to get maybe 15AH 3) my impression (data is hard to find) is that battery lifetime (number of charge-discharge cycles) gets much shorter if a battery is routinely discharged more than 50%. So I'm planning on using 50% discharge (7.5AH) on my flights. Although the 20AH size is more expensive, I hope the lower % discharge will give me a compensating increase in battery lifetime. At my draw of 1.8A, 7.5AH is a 4hr flight. So I should typically land with the battery still strong.