Battery Refresher
idea: Burkhard Kainka (Germany)
In the past, a sawtooth was often generated using no more than a small neon lamp and a capacitor, and the resuting circuit was called 'relaxation oscillator'. Less well known, the effect can also be achieved with an ordinary NPN small signal transistor like a BC547 as sketched in Figure 1 below. It is too much to explain here in detail how this can work – let it be sufficient to state that it works and we refer you to the original publication in Elektor's Project Generator Compendium 2011 (page 80) for the details.
Figure 1.