WAV50s have AGM batteries, which is why they are able to lay on their sides. I've found a trick to reset the BDI easily. Since the voltage passes through so many connections to get to the BDI it's a fairly common problem when batteries get older.

I have a car charger at home that I can set for AGM batteries. After I make sure the WAV's charger won't charge any more, I connect it to two of the batteries on one side on the positive and negative posts that are NOT jumpered to each other. Turn on the fast charge option and wait about 30 secs. With the charger still on, I turn on the key switch and the BDI is reset! The charger adds enough voltage to surpass the amount required for the BDI reset.

This trick was told to me by one of our Crown technicians and doesn't harm anything with the WAVs.