Volt/Bloog/V2 all = kr808-d batteries. Any cartomizer threaded for a kr808-d port will fit on any of them.
The voltage and amperage doesnt matter any as far as connectivity goes.
The 4.2 as said above will drop almost instantly to 3.7. This only measures how much electricity goes through the heating element, thus producing more vapor at higher voltage, all depending on the resistance of the element.
The 220/250 mAh amperage measures the battery's life span ... meaning the higher the amperage, the longer the charge of your battery will last before you need to recharge it. This will also affect the overall life span, meaning how long until the battery will not longer hold a charge.
Hope this helped.