Haven't heard of a 3300 going bad, but I'm sure it can happen.C7 US 3300 Battery Charger
Have issues? Battery went dead while sitting in garage once and hooked up this charger. Worked fine after an 1 HR. Two weeks latter battery goes dead again and I had driven it with in those two weeks. Ok! I plug in the charger and 12 hrs later still showing charge. I disconnect unit and try to jump start off my truck. It clicks a few time than nothing. Battery not taking jump. OK! So I call for road assistant, yes road assistance it free, first guy had no clue and didn't even try to jump start vehicle. Now the second company came out with a portable battery charger great (Im a x mechanic) now he hooked that unit up and still just a few clicks from the starter, so he attached another set of cables of his vehicle and it started. Now he said this was the third Vet he started this day. He says it take up 950 amp to 1000 amp to jump start these batteries. Also that US3300 got very hot while pluged in. I dont if that a problem. The booklet doesn't explain a lot. The power on was lite and the charging process waqs also on for 12 plus 6 hours. Maybe unit is bad?
You seem confident that the battery is not the issue... why? I had my first battery fail in the first few months of ownership, while the 2nd battery has been good for 2 years now.
Do you have anything plugged-in that would cause parasitic load, like a Range AFM disabler?