Here goes. I have three 36v 13Ah batteries for my ebike. One is 3 years old and the one that came with my bike. It is in excellent shape. I then bought two more from YosePower and they are about two years old. It’s these two I want to ask about. I’ll call them Y1 and Y2 to avoid confusion. They both charge up to 42v and show 41.9v when taken off the charger. Y1 then loses about .1v per day until it reaches 41.5v, then slowly to 41.3v after a week. I usually charge them up after a week or so. I haven’t messed with Y1. Y2 however, drops to 41.7v overnight and drops to 41.3v in two days. I thought it may have something to do with the Y2 BMS so I changed to a Daly BMS, but it made no difference. I then charged it up and disconnected the BMS and measured the cell groups daily. They all stayed at 4.0v and after a week all dropped to 3.9v. I realize that these may just be low grade batteries..BUT…since they are all connected, is it possible that some single cell in one group is weak and the rest of the groups are trying to charge it and slowly draining power? One other note. I tried buying one of those cheap active balancers but I have smoked two of them just plugging them in. Apparently this is a very big flaw with them and the manufacturer told me it can happen. Well gosh, I don’t want to keep taking that chance. So, if it is a weak cell, how to trace it? Any help always appreciated!