the D2 is better with other Small Capacity Batteries
When charging batteries with a capacity lower than 750mAH (e.g.
AAA, 10440 and 16340 batteries), a low charging current is
recommended to help extend battery life.
(i2 cannot do this)

To select a low charging current, while in regular charging mode,
simply press the side “SLOT” button to select a desired battery slot
and then press and hold the side “MODE” button for more than 1
second until “LOW” is displayed on the LCD display indicating
activation of low current charging mode. To exit, simply press and
hold the side “MODE” button for more than 1 second once again or
remove and reinstall the battery
(low charging current also works on all batteries)