My eCo charger is 1000mAh with 3.8v output. I have an older revision, so I don't know about the current batteries.
My Joye eGo charger is 420mAh with 4.2v output.
I noticed that what GP currently has, lists the eCo charger as 420mAh.
I can use the eGo charger for my eCo batteries, but the eCo charger does charge them faster. However, I can't use my eCo charger on my eGo batteries. The eGo batteries will do some bizarre things.