I had a bad ground from the LEDGLOW I had set-up as it was a continous drain according to my electrician. (I do have periodsat times to where the car would sit for a week to 3 weeks btw.) I had to say goodbye to the little Kinetix battery among previous Optimas Red and YellowTop, I also had to go with a high-powered alternator(well a stronger one than the rebuilt alternators out there for our car) and thankfully have been issue free since.
I did have the LEDGLOW reconnected to a better ground and connected safely as above mentioned technician did not secure their live wires while under the dashboard.
I know the Voltage Stabilizer is basically a capacitor, though I did not see it as a great help overall.
ParkerBro, does have a point as I would watch DVD's with the engine off knowing some are 90 mins, so I can see how that lead to problems at times too even with non-daily usage.
Best of Luck, hoping yourself and your cousin can find the source and correct it...knowing it took the electrician 2 days to go thru everything and determine the cause in my case (a bad ground).