This is my first battery, but not my only one. The Ego V has been a solid unit since day one, and lasts all day with HEAVY use. At first I wasn't sure about the adjustable voltage, but after playing with it for a while, I understand it's usefulness. Different flavors, taste different at different temperatures. Hard to believe but you CAN tell the difference between 3.5 volts, and 4.0 volts. The only things I would be concerned with about this unit are- Length: it's a bit long, but that is why it lasts all day. The power button is a bit hard to find (very recessed) at first but you get the hang of where it is, and it will NOT go on in your pocket. The little chrome cap on the bottom snagged on my pocket and popped off. Dab of nail glue, good as new! I would definitely buy another.