Charging Lithium-Ion Batteries – Battery University: "Simple Guidelines for Charging Lithium-based Batteries
A portable device should be turned off while charging. This allows the battery to reach the threshold voltage unhindered and reflects the correct saturation current responsible to terminate the charge. A parasitic load confuses the charger.
Charge at a moderate temperature. Do not charge below freezing.
Lithium-ion does not need to be fully charged; a partial charge is better.
Chargers use different methods for “ready” indication. The light signal may not always indicate a full charge.
Discontinue using charger and/or battery if the battery gets excessively warm.
Before prolonged storage, apply some charge to bring the pack to about half charge.
Over-discharged batteries can be “boosted” to life again. Discard pack if the voltage does not rise to a normal level within a minute while on boost. "
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