I have been using the AC10C for years and it is still functioning well. I really wonder what makes ur unit act funky....

It is possible that the charge control IC in the N900 sees a dip in the voltage and reduces the current but I haven't spend a lot of time investigating that. I don't even recall if the charging chip had some kind of undervoltage protection.

When I tested the car charger I didn't do transient load testing. It is possible that the car charger voltage dips when a heavy load is applied.

I have a long motorcycle trip coming up at the end of the month and I will report back. The best kind of testing is real world testing