Weekend cabin lesson, the battery was fine while i was there, the problem was the five days in between
We have a small weekend place a couple of hours out, no grid connection, and i spent the first month worrying about the wrong thing. I was obsessing over whether the panel and battery could handle a weekend of lights and charging and a bit of streaming, which it can, easily. The real problem was what happened to the battery between sunday afternoon and the next friday evening.
Setup is dead simple. One 400 W panel leaned against the south wall, a battery box of about 2.5 kWh, and a small satellite dish with a travel router that we only power on in the evenings. Friday to sunday we run LED lights, charge phones and a camera, a little USB fan, and maybe two hours of the dish in the evening. The panel refills the battery during saturday and we never dropped below about 40 percent. That part was fine from day one.
The surprise came after the first weekend we left everything connected. Got back the following friday to find the battery at 12 percent. I had left the router plugged in, not even on, just in standby, and a small 12 V DC timer for a water pump that was not running but had a phantom draw. The whole stretch was grey and drizzly, the kind of week where the panel barely puts out a couple hundred watt hours a day if you are lucky, so those two little loads ate nearly the whole battery. Fifteen watts continuous sounds like nothing when you are there, but over a hundred and twenty hours of rain and cloud it adds up to almost two kilowatt hours, basically the whole usable capacity.
So now i have a proper disconnect routine. Sunday before we leave i unplug the router and the timer from the small distribution block, panel stays connected, and the battery just sits at whatever state of charge it ended the weekend at. The panel tops it back up on the first clear day after we leave and it holds fine until friday. Last three weekends i have arrived to a battery at 80 to 90 percent instead of limping in at 12.
The battery is a Jackery unit, nothing fancy, and it does not have a low power storage mode or a remote disconnect, so i do it manually. If i was building this from scratch i would probably add a master switch on the DC side rather than unplugging things every sunday, but the unplugging takes thirty seconds and it works. For anyone setting up a weekend cabin, the question is not whether your panel and battery can handle the weekend, they can. The question is what you leave connected when you lock the door.