4 days is really about normal, when the clouds roll in I cut back on non essential power use but by Day 4 its certainly genny time, though I would run it earlier so needing a shorter running time to charge so less fuel used and less genny noise, (I hate the things) if you were running your tug to charge the batteries up each day it would be idling for a few hours and thats not good for it at all, especially if its a CRD ..................... soon as the clouds roll in then you go into power save mode, no invertor usage, no electrical gear left on stand by all shut down by switch, something that should be done all the time actually..... one phone turned on others shut down, a couple of phones on charge or left on charge will suck power.....
The only sure fire way is to have a genny really, while they are a pain they do save the day, when needed to charge the batteries you stay in economy mode for power usage and plug in the stuff you need charging into the 240 points while the genny is charging the batteries then when done keep power usage at economy rate till the sunshines again.......... My genny doesn't get used often but has been a god send at times especially when the Colorado battery died, the genny got enough charge in it to start and get to a town for new battery...it paid for itself that time.
My set up on rainy days will still manage to drag some power in but its no where near enough and if its really cold weather needing the diesel heater of a morning then my power isn't going to last 4 days at all...