Options:

Purchase an inverter that alarms only when actually needed - after all, alarms are there for a reason. Low battery voltage will damage both the inverter and sulphate the battery, altogether a stupid, wasteful idea. Go up to at least 500 watts. Most inverters do not like being run at even 50% of rating. And the incremental cost is tiny. Furthermore, the closer an inverter is run to its rating, the greater the lost-to-use ratio. So, by going to a lower-rated inverter, you are draining your battery that much faster.

https://www.potekelec.com/power-inve...CGIwQAv D_BwE

https://www.amazon.com/gp/offer-list...&condition=new

Purchase 'resist' lacquer and coat both the slots on the case and the traces on the board. This can be done as either a spray or a pen. This may salvage your existing device.

It is really not a good idea from a life-safety position to run an inverter without the cover. A modified square wave is far more damaging than a pure sine-wave - and you are no more than a 10,000 ohm, 1/4 watt resistor assuming you are otherwise entirely healthy with no compromising medical condition.

Peter Wieck
Melrose Park, PA