What I have ended up with is a very light (around 3kgs) 21Ah useable box with 2x 5v / 2.4 Amp USB, 1x Engel, 1x Cig, 1x 240 Outlet using a 24v 600w Pure Sine Wave inverter. The battery I built using 18650 cells and is 24v so I have a BMS on it, a DC / Solar Charge controller feeding it that can step up and step down the power as required for the battery, a 24v to 12v buck converter and a shunt to measure whats coming out of the battery.
I will be attaching this to my solar panels and fridge, so i was wondering how you go about controlling the discharge and charge at the same time? I assume that all outputs go through your buck converter, and any input to the battery goes through a charge controller? So all power going out pretty much goes through the batteries first? Everythign else i am pretty good with, it is the simultaneous charge/discharge i am yet to get my head around.
Great looking project!