One charging technique I have used is to alternate charging the batteries on the "normal"/lower-rate charger (which comes with the 5.0 ah and smaller batteries) and the "fast" charger (which comes with the 7.5 ah and larger batteries). Using the slow-rate charger seems to extend the life of all different ah batteries. I have (2) 7.5 ah, (2) 5.0 ah, and (2) 2.5 ah batteries for the full suite of EGO power equipment in my arsenal (mower, line trimmer, edger, hedge trimmer, power head w/pole saw, hedge trimmer, and extension attachments, 530-cfm blower, and snowblower). Most have lasted 5+ years, although I needed to warranty (1) 2.5 ah battery, which was an older design.