Whats normal voltage drop from a 4amp load? (210ah)

Turn the fridge off before cranking up the voltage past 15.4v, the spec high DC limit for fridge. Also the inverter will (depending on specs--some have a 15v limit) reach its high voltage limit so no 120v if you do this with solar.

You need to start the equalize with full batteries, which is hard to have off-grid while using the batteries. If you had four 6s , you could split the bank to run the rig on two and fill, then equalize the other two. Then next sunny day, you can do the other two.