Yes, it augments input with battery power if input < load. So if input = 0,then it's all coming from the battery. I've unplugged a solar panel with a load drawing roughly 150 mA at 5V and the switch to battery power did not cause any power blip, thanks in part to that huge capacitor on the charger. I'm not 100% sure if the opposite is true, that is, any extra power the load does not need goes to charging the battery. I believe the answer is yes, but I'm not sure at what threshold. i.e. how much leftover do you need to charge.