Hello, I am new to the forum but I thought I would join as I am very interested in off the grid living. I live in the UK in a very rural area. I thought I would post some pics to explain the project a bit more but also bring a human element instead of my saying why doesn't it work So the task at hand it a Hut.... I will cover other bits later but my problem at the moment is the power. 2 250w Solar panels provide power at present. I must add power demand is minimal, for a water pump 1kw which rarely runs and a 240v circuit should it ever be needed. These go into a not great charge controller but I accepted a little inefficiency when purchasing. I believe this is 33 percent less efficient that a modern one.. But still as you can see 18amps is going into the controller. As you can see above the battery percentage is 72 percent (this is worth remembering later). I haven't hooked the LOAD up to this charge controller as I don't think it is adequate for the potential pull from the inverter. So the load comes straight off the batteries. This charges 2 250AH deep cycle batteries via the controller. These are 12V batteries in Series with the inverter connection coming from the positive on the left battery and the negative from the right battery. All of this goes to a 3KW inverter (pure sine wave). Note I have increased cable size to that of the large black one below and not the small red one I had originally. I have also added the earthing cables since the picture was taken. Note the switching box allows for mains (if I ran an extension cable up to the hut and plugged it in) or "2" which is batteries below. So everything works as it should... I was concerned about the gauge of the cable going from the batteries to the inverter, so despite it working I went for the biggest cable I could which is for welding and meets the spec of 400 amps which the inverter could pull (but never will in my scenario). I also reduced the length of the cables, I think the longest is about 2 metres which should be well in the safety range. I did have some issues with the connectors for the cables, I wasnt sure if they were up to the potential amps going from 12v to 240 but the fuse below gives me a safety element. They are the biggest the electrical place had, I had to hammer crimp them on then drove a nail into the middle to pinch it. To be extra cautious I added a 100 AMP fuse on the circuit between batteries and inverter. The Problem So the charge controller tells me the batteries are at 99 percent (which is max) in this state no power will be sent from the panels to the battery. As soon as I turn the inverter on (even with the master hut power set to OFF) the battery drops to 72%. I left this on for a couple of days and it was at 68%. Is this a problem? Is this due to the cables (I cant see how it could be) or is it down to the fact the load for the inverter doesn't go through the charge controller ? Should I be worried about this ? The inverter when it is on does produce some heat which I accept (the cables are cool even under load) and the draw should be minimal. the 250 AH batteries 2 will have 500 AH in them and are brand new so I don't understand the 28 percent drop ?