Trouble with TP charger, question about hyperion charger

[Slowkrawl]

Hey guys, a buddy of mine picked up a thunder power tp610c charger today, and off the wall plug it runs for a couple minutes then turns off, and back on. But off of a 12v car battery it works fine? kind of an odd problem, I am thinking it is a lemon but hoping one of you guys can help us.

Also, my hyperion720i charger will only let me charge a 4000mah lipo at 2c, when it is rated for up to 8c. The charger should do 20a(not that i will charge it at that...). The power supply should put out 12v at up to 30a(according to feathermerchant rc). Is the PS not big enough or am I missing something?

Thanks for any help guys.

-Matt