Well you shouldn’t empty your lipo cells in the first place! Believe me you only damage them doing so. This fix sometimes (not all times!) works and even if it works you loose some of the lipo’s capacity.

I discovered it when I damaged a lipo pack in a transmitter that I left on over night. It’s an old transmitter so it didn’t have any timeout build in. Too bad it happened with a brand new 2200mah pack :s. I have a simple Turnigy 2-6 cell charger and it would only show me the “low voltage” error on any lipo setting. This is how I fixed it:

• Load it carefully using the NiMH program up to a save voltage according to the amount of cells. That is only 6v for 2S, 9v for 3S, etc. Keep an eye on your pack, it shouldn’t get hot! For safety you could use a special lipo bag.
• Set your charger back to LIPO and it should charge now. If it still doesn’t work you can as well toss your lipo away. Discharge it completely using a 12v automotive light bulb, take it apart and throw it away.

Most ESC’s (check yours to be sure) have a built in lipo saving feature so they don’t drain your lipo battery below a certain voltage. If you don’t have these or just need another way to make sure your lipo is cut off on time you can go for a battery monitor.

The cheapest solution is the battery monitor with a simple alarm (sound + led) when voltage drops. Check Hobby King Battery Monitor 2S, 3S, 4S, 5S or 6S. They all go off on a different voltage based on the amount of cells in your pack. Make sure to match or this is just no use at all.

If you don’t really need the sound and can live with a bright led only you could go for the HXT 3S Lipo monitor or the HXT 4S Lipo monitor.

Another slightly more expensive solution is one of the all in one battery monitors that even come with a display and work with 2 to 6s lipo’s.

And keep balancing your packs while charging. Discharging your pack to its normal level when you have an unbalanced pack will cause one cells capacity/voltage to drop too low, resulting in a faulty cell which will very quickly reduce the packs performance.

A properly balanced pack can last 600 cycles or more. However, unbalanced packs rarely make it past 100 cycles before at least 1 cell becomes faulty.

Happy Charging!