For my RGB trampoline project, I had the unique issue of having a dozen batteries to charge at once. This usually meant filling up the phone chargers in the house and playing merry-go-round after a few days of use. In this project, I build a charger that will fit and charge all the batteries for the project at once.
I used the following meter for check the voltage and current.
The STL and SVG’s for this project can be found in my Cults3D profile here.