As summarized on this page: http://www.hypershop.com/HyperJuice/External-Battery-for-MacBook-iPad-iPhone-USB/
HyperJuice 1.5 has a 4 stage LED battery level indicator showing the battery levels at 25%, 50%,75% and 100%
HyperJuice 2 has an advanced OLED display showing the battery level in percentages (0-100%), battery status (idle/charging/discharging), battery temperature (in degrees Celsius and Fahrenheit) and remaining time for battery to be fully charged or discharged
HyperJuice 2 also has user replaceable/upgradeable components. The aluminum casing, battery cells and logic board can be bought separately for replacement or upgrading.
Lastly, HyperJuice 1.5 is available in 4 different capacities (60Wh,100Wh, 150Wh, 222Wh)
While HyperJuice 2 is only available in 100Wh capacity.