Battery Pack Degradation
I look at a lot of packs during a month's time, generally because the racer has experienced a performance problem or a mechanical problem on the pack. In all cases, the question is whether the pack is at fault.
In order, these are the recurring issues I see and their cause:
Pack Swelling - Discharging pack below 6.3v (2S pack). The closer you get to 6v, the greater the swelling will be. May not happen immediately, but within a few days.
Higher than normal pack temperature - Several potential reasons: a) Loose connection on the pack generates resistance and high temperatures b) Gearing motor too high which results in high discharge rates 3) High Charge rates eventually changes the internal makeup of the cells, resulting in accelerating internal resistance increases, and high pack temp.
Mechanical Pack Damage such as loose pack terminals or case being melted (see above) - a) Loose connection at the bullet connector is the number one cause. Change your bullet connector frequently to keep these connections tight. b) See Item 2 above.