Took a shot at reducing the case size. The large version(7"x5"x2") is good for 7.5 hours, and is nearly indestructible. The small case is a tiny fishing tackle box, the size of a match box(5"x3"x1.75"), good for 2.5 hours. I've left a USB cord attached to it, so it can be plugged in whenever possible. Decent for trips to the gym.
5" long is as small as you can get and fit the Dexcom with it plugged in. Had to special order a 90 degree micro usb plug.
A picture of the inside of the box. The battery is underneath. The switch allows me to charge the battery while still running the PI. Not sure what's with this brand of battery/charger circuit(enercell), but it shuts off power when charging. The PI has been extensively modified. I've cut off just about everything that sticks up. Also, relocated the USB ports. Allot of time was spent with a magnifying glass doing this work. I've also shortened the numerous USB cables. You run out of room fast with extra cord length. USB plugs were also shaved with a razor blade to make them lower profile, and more bendable. Power is supplied to the PI via the GPIO pins, since I didn't have another 90 degree USB. Also removed the case from the battery, which freed up 1/8", allowing the Dex to sit on a plastic plate, and not directly on the circuitry beneath.
Did some additional tests with the Chronos, battery life is shorter on the transmitter side then using bluetooth. So the Chronos is entirely out of the picture now.