My original pair of Makita L-ion batteries are 5 years old now and are still pretty good and its looking like they will outlast the drill (BHP541) which is pretty tired now, I use it every day and probably charge each battery 3 times a week on average.
One thing I do is not leave them in the van at night when its cold or during the day when its really hot.
I agree. I got the first generation Makita lion and the batteries, and the tools are still going strong. I burned through a Dewalt 18V Nicad in 4 years. The batteries went and then the gearbox on the drill.
One thing about the Makita though - when I bought the set I got a coupon for a sawzall and I can only say that I've been disappointed with. No speed and no power.