Yeah, HK has a fairly high dud rate. In my case a batch of 4s packs were all dead by two weeks. Couple cycles and puffed like mad. But not one dud out of the other 20 packs I've bought. Still cheap despite a few duds. In general, a dud shows itself fairly quick, so once you sort the good ones out, you can count on them for some time.
Unless you go kill em.
Let's not dwell too much on the other packs I noobishly killed.
There's the real failure rate, my failure to learn not to short the leads. Took awhile, but I stopped kff ing. Since I got started, some better foolproof wiring harnesses got invented.
The smart set just buys 9 packs to make an 8 pack bike battery. One thing though, you really must sort out the duds before you start doing anything permanent. It's one of the reasons my lipo setups are deliberately non permanent. Any wonky pack is sorted out and replaced with a good one in about 10 seconds.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE
Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum
See battery technology section, FAQ thread at the top of the page for lipo noob info.