I am using two Lithium ion tool batteries (18V) to get a 36 V line. When fully charged it is greater then 40V. As they are tool batteries, undervoltage protection is already built in.
I want to be able to charge these batteries with a very high voltage solar panel (>50V). I am not interested in efficiency. I am only worried about overvoltage protection for the batteries.
Is there a cheap way to have charge protection with this system. The application is audio, so violent audio band waveforms (< 24 kHz) is not acceptable on the power lines.