> if one could expect a 100% efficient converter, is it not realy > the V x mAh value that is interesting, not ? You mean comparing the batteries in terms of mWh ? In the end I suppose it boils down to the number of electrons available and the internal resistance of the battery. But I wouldn't know where to take it from there. The practical problem is the step-down efficiency -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist