Initialy it was intended that the lantern would be powered from 4 AA cells. 4 rechargeable cells offer 4.8 Volts@1200 mAh. 6 LEDs at full power consume 50 mAh each so 300mAh for the lot. Add 100mAh approx for IC and total current is 400ma giving 3 hours of light.
However, why create a battery enclosure to accomodate 4 cells, as this would make the enclosure more complicated to build than if only a single cell was to be used with a dc-dc step up to 5V for the IC? A nickel D-cell can hold up to 5Ah at 1.2 Volts. So at a maximum current of 5/1.2=3.3 times 400mA = 1.3A. 5/1.3=3.8 hours, so a bit more power as that obtained from 4 AA cells.
Re-dimensioning for a D cell, I came up with:
