AcesSmokeShop

Hello everyone. I was hoping I could use some collective knowledge here to help me out on an issue. I have a vape shop and a particular customer seems to have an issue with his 18650 batteries. He claims that every 18650 battery he gets from me dies after only a few charges. My first thought would be that it was perhaps a bad batch of batteries I got from my vendor, but he is the only person having this issue. He has tried several chargers. I know he's using a rebuildable, but that's all he knew enough about to tell me. My question to you guys is what could he possibly be doing to kill these batteries if it's not the charger and not a bad batch of batteries?