The problem is that almost everything on Ebay and Amazon with the word "battery" in it is fake
Even if the advert says "Pentax genuine" or "APC genuine" (for a UPS battery) and is close to the full price, it is likely to be a fake, IME.
The only reliable way to get genuine batteries is to buy them from a Pentax (etc) dealer.
I have used Hahnel and it worked well enough in various Pentax cameras, with about 75% of the capacity of the genuine Pentax one. It failed after about a year but an email to Hahnel produced the offer of a free replacement, which is pretty good. I now use it as a backup (I tend to alternate the two).
I didn't know there was an AA container for the K1 battery. Can anyone recommend one which fits well? The ability to use Eneloops was why I kept the K200 (?) for a long time. This, I find, is not a great operational issue because I can shoot hundreds of pics on a 1 week trip on one battery, usually, and with the 2nd one I have not had a problem. But I do mostly "landscapes" and can easily see somebody running out if they shoot action.