This circuit is an alternative to expensive battery chargers, the trick to lower the cost is to buy a cheap battery charger and expand it with an automatic charge breaker circuit such as the one ...

I designed a compact, standalone Li-ion battery charger that is simple to build, extremely affordable, and easy to integrate directly into projects.

The following automatic battery-charger design is created with a circuit that could qualify as the simplest window comparator ever built around a single transistor (see the figure). It starts charging ...