Now lets design a Battery Charger circuit.

I decided to use a TP4065 over a TP4056... No this is not a typo.

Due to some research on twitter I got the hint that the TP4065 is smaller in the footprint and has a way lower quiescent current than its brother the TP4056.

But where to get this little beast.... This was a very hard mission. Everywhere you search for TP4065 you will always get search results for TP4056.

Luckily I found some parts as a leftover stock at LCSC.

What is the Magic about this circuit:

You see this MosFET next to R33. Once External USB Power is connected this MosFET prevents that any power is drained from the battery.

The Voltage from the battery is completely shut down. The Battery is still charging but no current is consumed out of the battery.