Solar Charge Controller
I’d like to build a charge controller for managing different battery voltage configurations without too much hassle.
References
Chips
If we don’t want to do “everything ourselves”:
- BQ25792 - I2C controlled, 5-A, 1-4 cell buck-boost charger with dual-input selector and USB PD 3.0 OTG output 
- BQ25798 - similar chip but with MPPT 
Other projects
 
 - BQ25798 - similar chip but with MPPT 
 - DIYODE Magazine - ATtiny85-based Solar Charge Contoller
 - Adam Welch - PWM85 Solar Charge Controller (also on Tindie)
 - Solar Energy Generator - hackaday.io
 - DIY Charge Controller - hackaday.io
 - Arduino MPPT Solar Charge Controller
 - SolarCharger SZBK07V2
 - High Efficiency MPPT Solar Charger
 - SunBoard - Charge Controller with MPPT & Bluetooth
 - Mppt Solar Charge Controller 12V
 - Skagmo - Maximum power point charger for solar panels - Github Repo
 - Solar/LiFePo Multi-Controller with MPPT and ESP32