Originally Posted by
Burton
Personally I've been using and working with NiCAD and NiMH rechargable batteries for about 30 years and Lipo and LiFeO4 batteries for about 6, and have had numerous discussion with reps on behalf of clients. The biggest issue NiCAD had was capacity, but it takes sophisticated chargers to avoid a memory effect in those. NiMH batteries actually lasted a lot longer before companies got into the capacity competition. My oldest batteries were made by Sony and are still going after 15 years - which really doesn't matter because they've been discontinued. The higher capacity replacements never lasted more than 4 years.
Same for Lipo and LiFeO4 chemisteries. It depends who makes them, how the battery management system controls charging, and how many cells are in the pack. Low charge rates still consistantly result in a longer life expectancy. Yeah - storing any battery at low temperature will improve life expectancy, but there's not a chance you can store any lithium ion lithium polymer chemistry battery at 40% capacity. The available capacity of those batteries is only a percentage of the total capacity and discharging or allowing it to discharge below typically 3.0V will result in what would appear to be a dead battery to most consumers.
40% of current capacity (not rated capacity, but current capacity) is the usually recommended way of estimating proper state-of-charge for storing lithium-ion batteries. 3.75 volts is used as an approximate guideline.
www.batteryuniversity.com has a section on battery storage.
There are various other technical points on all this, but I don't want the primary focus of the thread to get lost or swamped by too microscopic a focus on technical minutiae.
Some points do have clear practical applications, and are worth mentioning though -- one of them is that prolonged heat will dramaticaly shorten the lifespan of batteres.
On a long bike tour it would be best to keep them where the temperatures will not be too high.