I fail to see how charging a battery will affect lights that aren't turned on. Now maybe if you tried to start it with the charger on and your foot on the brake pedal. But even that sounds unlikely. I'd have asked him to explain it to me.
Me too... Especially with LED's. It takes a lot to kill one of those, and I'm not sure your battery/charger has the oomph to do it.
You've checked your grounds, yeah?
