Amazon.com : PENTAX Battery Grip D-BG8 Black for Pentax K-3 III Flagship DSLR Dust-Proof and Weather Resistant Construction with Capacity to Hold Additional D-LI90 Battery (37048) : Electronics
Pentax K-3 II battery: what are the options?
AliExpress
Amazon.com : Wasabi Power Battery (2-Pack) and Charger for Pentax D-LI90 and Pentax 645D, 645Z, K-01, K-3, K-5, K-5 II, K-5 IIs, K-7 : Digital Camera Batteries : Electronics
Review: Pentax K-3 II offers useful new features
The Pentax K-3 II Scores Big Points on the Nature Photographer's Camera Wishlist | Fstoppers