I have both a Mixpre-6mki, and a Mixpre-6mkii. The AA battery holders that came with them are identical. Sound Devices may have redesigned them at some point, but the Eneloop Pro batteries I use fit both samples I have just fine. I read that you can remove the center rib in the holder if you have oversized batteries you want to use, and the holder will latch to the recorder properly again.