I'd get this battery grip (exact replica of Pentax original - you can even trade the battery trays between them (I have one original and one of these)):
Battery Grip For Pentax K7 K-7 DSRL D-BG4 - Newegg.com
Then get extra batteries - eneloop, energizer Ultimate Lithiums, or more K-5 batteries. Cheap (relatively) and easy.
For external batteries I use Anker from Amazon. If you need to go bigger, like to power a notebook or give an iPad a full charge, this guy is good (he's been doing it for years, he's into it, he has some of his own designs made for him in Asia, and he'll get you or make the right connectors if possible. He's local so I've talked to him in person. Seems expensive until you realize how much capacity they really have - then you see it's worth it.):
External Battery Pack for Apple MacBooks and iPad/iPhone -MAC90
You can buy from Bixnet directly, and if you call, the owner (tech guy) often answers. You can also buy from them on Amazon. He may have ideas for all of your external power needs, if you just tell him what your devices are.