It took all night to charge my ego 900mah on my computer port when I first got it. I thought I had a crappy battery or port, then I researched it and the computer USB port is crap for charging
batteries and furthermore since the USB port is directly connected to your motherboard and if that ego battery farts while charging it could blow your mothrboard. Once I read that I now don't charge no IPhone/IPad nor ciggy
batteries on my computer USB ports.
It should take bout 2-2 1/2 hours to charge a 900mah battery on a 420 mah/hour charger Just look at the micro print "output" on the charger to see how many mah/hour it puts out.
The one I got with my Ego is 420 mah/hour and another wall charger we bought is 500mah so do the math.
I bought one of those variable voltage USB passthroughs before I came across the blowing of motherboard article, so I now use the passthrough in a powered multiport USB adapter and have it plugged into the wall but not into the computer and it works like a hot damn. I can puff all day sitting at the computer and not use a iota of battery.

I also modified the little stubby passthrough with a plastic 5 gallon pail handle so its nice and big and its bout the size of a couple 18650
batteries stacked up so its nice to hold. Also great for in the car cause your not using batteries and having to try to charge them using your cars USB ports inwhich prolly has the same wreck something if the ego battery farts during charging, or have puffed out batteries at your destination.