I have actually been happy so far with my experience on HK returns. One of the batteries out of three wouldn't ballance, (Nano tech 6s 35-70c 3.3 amp packs). I discovered this a couple of weeks after receiving them. Took pictures showing the charge results and sent the item back. Credit was issued one week later and I ordered a new one from the US warehouse. Have over 90 flights on these batteries. They do get warm after and swell only slightly and by the time I recharge them the swelling has gone.
One of the newer batteries that I've been using from HK is the Nano tech A spec 2.4 amp 4s 65 -130c rated battery. I have abused this battery by over pulling to many amps out of it the first use and it was warm+. I actually found out the under load I was pulling cells down below 3 volts (duh), but the pack came back without a hitch and takes a full charge. No puffing and I've used the pack now more than 30 times for full flights. [8D]