For safety consideration, our li-ion battery pack has PCB protection which will protect the battery packs from over charging and discharge. When the li-ion battery is over charging or discharged, the PCB will cut off automatically. Then you may find the battery pack is 0 voltage. This doesn't mean the battery pack is dead. You can just use our charger to charge it, everything will back to normal. Please make sure to use batteryspace's recommended chargers. We are not responsible for other brand chargers. However, this is not applied to battery which hadn't been charged for more than two months. You should charge battery every 2 months to keep it fresh if you don't use it.