I don't agree. 5V 300mA is more tan enough for 2 1.5V batteries. Just add a low drop regulator. I have 6 x 7.5V x 200mA film panels of slightly larger size each (still almost unnoticeable for EDC). They're recharging my 3600mAH LiIon powerbank, rated 12V-30V of charging voltage, in about 5 hours, just laying flat on the table. I'm recharging most of my EDC electronic gadgets from the powerbank (regulated output 1.5V-12V every 0.5V) after that, including 4 AA cells, but excluding my UMPC.