I have a mercer 1000va/720w inverter with a discovery dry cell battery. It worked well until is started struggling to switch over/on once the mains switched off. I used the age old 'slap on the side' method which worked and I assumed a cable might be the culprit. I opened up the unit, gave it a clean and checked the wires. Sure enough, fiddling with the wires works, sometimes the wire to the little circuit switch and sometimes the wire to the display. But as soon as I replace the top cover, it slap is requited once more. It is a very bare bones unit and the display has no menu options. I've tested the battery and have it on a smart charger at the moment. Has any issues like this been reported before? Thanks in advance.