I have been wondering about storing my bike outside in the cold New England winters. Here’s a great post that talks about that, and other storage, temperature and charging issues with lipo batteries from none other than the RC aviation community. Who else?
He focuses on getting the most life out of lipo, and the secret is in not abusing them… knowingly or not.
Lithium lifetime is based on several factors:
1. Temperature while in use
2. Temperature while in storage (for our purposes, “storage” is the same as “maintaining a constant voltage level”)
3. Percentage of “full charge” (4.20v/cell) to which a cell is charged
4. Percentage of “full discharge” (depending on chemistry, somewhere between 2.5v and 3.2v) reached by a cell
5. Rate of charge (depending on chemistry, between 0.3C and 3C may not be excessive)
6. Rate of discharge (depending on chemistry, up to 20C may not be excessive)
7. Charge level while in storage
In particular, there’s the issue of charging when the batteries are cold. And by cold, he means around 32F. If you top out the battery at that temperature, you’ve overcharged it. When it gets warmer, your 4.2V charge is going to go well over that, apparently, so you may have taken as much as 10% off the life of the pack.
Here’s another very informative post on lipo use in general: Lipo Usage Best Practices.
Finally, none other than Battery University:
Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F). Although the pack appears to be charging normally, plating of metallic lithium can occur on the anode during a subfreezing charge. The plating is permanent and cannot be removed with cycling. Batteries with lithium plating are known to be more vulnerable to failure if exposed to vibration or other stressful conditions. Advanced chargers, such as those made by Cadex, prevent charging Li-ion below freezing.