Actually if you follow their warranty rules (register the packs within 24hrs of receipt) and if there is a voltage prob, you do nothing - you do not attempt to charge it or anything else, you get an RMA and send it back at your expense and wait.

I usually buy extra lipo if the lipos are critical, so I can tolerate a bad one, not sure I'd send one back either. The plane guys seem to return low voltage ones all the time and after about a months wait, they get new replacements. They follow the warranty/return policy to the letter. This is posted about a good bit on RC Groups. HK has gotten a lot better in the last few years though.

I started by buying a pair of HK 3S lipos and one was low voltage right off the bat. Now 2 yrs later, I've bought 8 more and they've all been good, so I'm 1 bad lipo out of 9.