I second the suggestion to use an RC multiple use charger. I use mine to rescue dying batteries of all types, as well as to put a controlled charge of any amount of current that I select. Mine cost about $70, is probably Chinese, and has a 12v power input, or use the onboard 120v converter with a regular plug.
The premature death of many of my power tool batteries seems to be caused by not having very smart chargers. The cigarette lighter type of plug in chargers only seem to work well when there is a built in regulator in the device itself. With an RC charger, you have the option of balancing the cells, which will quadruple the life of any multi cell lithium battery. Amazingly, many chargers don't consider this, and just slam all the cells with the series voltage.
