The FF-ESP32-OpenMPPT/OpenMPPT-HP devices are open-hardware and open-software batterycharge controllers for photovoltaic solar modules with maximum power point tracking (or MPPT, for short). Together with a decently sized rechargable battery of 12Volt (typically AGM lead acid) they can provide autonomous DC electricity. This open-hardware and software development project was initated by Freifunk in 2017 with the first OpenMPPT version, based on a 8-bit Atmel AVR Mega8 microcontroller.