I had the exact same thing happen to the zeel in my SJ with a charging system. I let the ski sit for about 3 weeks between rides and the battery went down to 5v. Put a 12 amp charger on it to bring it back overnight. Got it cranking but no spark. Turns out the 3v zeel fuse blew. I replaced it and it held, but still no spark. I contacted Borut directly and he warrantied the zeel. I am back to stock 62t until I get the new one in the mail. My buddy is having a very similar issue in his charging system too. He has intermittent spark with no resolution so far. Sometimes it works, and sometimes no. I have had great luck with the unit in my 967 so I am hoping my luck holds up.
Ohh yea, I checked my charging system in my SJ and was reading 13.1 v at idle. Voltage was still climbing before I killed the engine so it would not get too hot.