You could try repeating the problem by taking a time lapse, I dont have this camera but I think it does it. A picture a minute for 5 hours maybe. check the time stamps on the pictures from when it went wrong, to see what load it was under and increase it a bit.
Also somewhere on the web is info on expanding 3party batteries, so that maybe a factor. You could try testing for this as well maybe.Given it has gone wrong then it def has a fault, and the motherboard most likely will be where any dry joins are, is my guess.
edit: Have you an estimate in your business plan for how long your eqipment should last? (aka how long is a pieceof string). sounds like you need to purchase another body, saying this could be well anoying as it is going to be tricky to earn a ton of money as a photographer.