I've had some comments from pre-release customers and #LiFePO4wered/USB customers about the poor fit of the LiFePO4 cell in the battery holders. The LiFePO4 cell is a millimeter or so bigger than a standard AA cell and caused the battery holder to warp.

I'm glad to announce that I have qualified a different battery holder, which provides a better fit for the LiFePO4 cell. It's still snug, but the plastic hardly warps and there is extra plastic holding the battery in the holder very securely. In the picture below, the new holder is in front and the old one in the back:

All pre-release customers will from now on be receiving units with the new holder. The remaining units with the old holders (which work just fine as well, but look a little less good) will be shipped to customers of the early-bird release sale. :)