I have the white and black Makita combo that I bought whenever it was that they first came out with them. They have the "half sized" 18v batteries. I'm thinking they are 6 or 7 years old, but don't really remember. 3 or 4 years ago, I bought the LXT combo, which has the full sized 18v battery. That was before they came out with the brushless ones. Both of the impact drivers have driven in several hundred pounds of screws, and the LXT some tens of pounds of the good sized star drive lags.

Just a couple of months ago I realized that I hadn't used the lightweight white ones in a long time, so I tried charging the batteries fully expecting that they had been sitting too long, and were old enough not to take a charge. Sure enough, the charger gave the blinking light drill for defective batteries. I had laid them in a window sill of a South facing window in an old house we were working on. Big Mike saw them sitting there, and put them back in the charger without me noticing him doing it. Both charged back up. Mike said that they were really warm when he charged them. They've been working like new ones for the several months since then.

I don't know which part, or parts, of the process worked, but there's no question that it worked. The LXT's are still working fine, and we use them most days.