Paul writes -

I got one of those battery extenders the other week and have been working through several years worth of “dead” batteries. At $40 for the device, if these all get used just once more, it paid for itself. And I assume I can get more than one re-use out of each one. Admittedly, each additional use cycle will be shorter, but if offered a 90¢ return on each dollar, then 75¢, then 60¢, then 50¢ etc. who wouldn’t take it?

Battery charger – it paid for itself – Link.

From the pages of MAKE:

Everything you need to know about batteries, and then some. MAKE 11 – page 151. View it now or subscribe!