I have been off the grid 6 years and now my system does not want to provide power at night (when source disappears). Batteries (4x 200A12V deep gel cell) do charge and during day all seems fine but problem seems that the moment power use to switch to batteries the system goes down. Could this be the result of a fuse. If so which one most likely. Who can I contact to assist (lockdown considered) or any assistance on what to do appreciated?