A battery is considered dead when it drains to a charge near zero. While a battery with a charge of just under 11.5 volts does likely not have enough power to start a vehicle, it is still not completely dead. But when a battery sits too long at a deficient charge (below 11.5V), it will soon become completely dead due to internal sulfation. Unlike most other battery types (especially lead acid), lithium-ion batteries do not like being stored at high charge levels. Charging and then storing above about 80% hastens capacity loss. Most Markus Unread wrote: "If you don’t know how long it will be stored, your safest bet is to do a full charge before storing." Hi, it is correct for Ni-mh battery, but certainly not for Lithium battery. The safest storage is between 40 and 60% of capacity. For example, Lithium-Polymer works between 3.0V and 4.2V with 3.7V of nominal voltage. Connect the main plug of your LiPo battery to your NiMH charger and start charging at the lowest current possible. Typically this is 0.1A. If your charger allows you to select the voltage you should select a voltage the matches your LiPo battery’s nominal voltage. After a minute or two your battery should recover to about 3.3 volts per cell. Lithium-ion batteries don’t last long if you let them drain and recharge completely, so you can keep them between 20 and 80 percent if you’re a heavy battery user. Older laptops with NiMH or NiCad batteries must drain completely to last longer because of the memory effect. If these laptop batteries die, you can try detaching and freezing them. Key Takeaways. All batteries slowly discharge their stored energy when not in use. While you can't avoid self-discharge, proper storage can slow it down. You charge a tablet or a battery pack for your power drill to 100%, put it in a drawer, and forget about it. The next time you pull it out, the battery is dead. First, fully charging a battery will shorten its lifespan. Second, a fully charged battery exposed to high temperatures is more likely to degrade or explode. Instead, store batteries at roughly 50 How to revive DEWALT Lithium battery? Not charging? If jumpstart won't work? try manual reset. I will show you how I fix or revive my DEWALT Lithium batter If your 3.7v lithium-ion battery’s voltage drops to below 1.5volts, it’s dead. Most lithium-ion batteries have a nominal voltage of between 3.7v-4.2v. The minimum safe voltage is usually around 2.7v, and the manufacturers normally indicate it on the manual. When the battery goes below the indicated minimum voltage, it’s dead. Temperature: The warmer the environment while a battery is in storage, the faster the rate of self-discharge. For example, a battery being stored at an average temperature of 80℉ will discharge at a rate of 4% per week. Whereas a lead acid battery being stored at 65℉ will only discharge at a rate of approximately 3% per month. M51FA.