As temperatures rise, you may find that you use your battery-heated items less. Don't just throw them in a drawer until next fall; follow these simple tips to extend the life of your rechargeable Lithium-ion battery.
First, let's look at how Li-ion batteries work.
The lithium-ion battery performs when ions move between the positive and negative electrodes. In theory, this system should work forever, but cycling, elevated temperature, and aging decrease the battery's performance over time. Manufacturers take a conservative approach and specify the life of Li-ion batteries in most consumer products as being between 300 and 500 discharge/charge cycles or two to three years, whichever occurs first. One charge cycle is a period of use from fully charged to fully discharged and fully recharged again. Over time, this process wears out the cathode, which results in reduced capacity. A high-end lithium-polymer battery can lose about 20 percent of its capacity after 1000 charge cycles. And batteries degrade even if you don't use them.
Similar to mechanical devices that wear out faster with heavy use, the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge of the battery is fine. There is no memory, and the battery does not need periodic full discharge cycles to prolong life.
Avoid heat, which degrades the batteries. Storing your heated items and their rechargeable batteries in your car or trunk until fall is a recipe for a bad battery! Always read your owner's manual to check their instructions for your specific Li-ion battery.
If you are planning to use your battery-heated apparel immediately after you finish charging up the battery, a 100% charge will have very little impact on your battery’s lifespan. However, if you leave your battery unused for many weeks or months, a charge level of between 30-60% is much healthier for the battery. Set a schedule in your calendar to periodically use the Li-ion battery in your heated products and then charge the battery again.
If you go to use your heated item next fall/winter and the battery has no charge remaining when you check it, consider the battery to be dead. Replace with a new battery.
To sum up:
Do not store your battery in a hot area.
Charge and discharge your battery on a regular basis over the summer.
Accept the fact that your rechargeable battery will eventually need to be replaced. Rechargeable does not equal eternal.
Read your owner's manual.