There are a couple of similar versions of so-called eGo-T
batteries. I've studied them, but not used them.
eGo-T LCD 1100mah Battery - Smoke Anywhere For Penny's, LLC Store
The lcd version is unregulated, and reads the current battery voltage. It also has a simple battery charge indicator on the side of the lcd. The votage will be around 4.2 volts fresh off of the charger, and will drop as the charge level drops. Probably to around 3.2-3.4 volts when it needs to be recharged.
There is an LED version that is a pseudo-variable voltage:
EGO 900mah Variable Voltage Manual Switch Battery
This has two regulated modes, at 3.4 and 3.7 volts. The 4.2v setting is just unregulated mode, and will act just like the model above, dropping in voltage as the charge depletes. I'd guess that the 3.7v setting will also drop when the battery gets below 3.7v.
Neither will hold a candle to the eGo-C Twist's true, buck-boost, variable voltage regulator, which can be adjusted from 3.2-4.8v, and holds the voltage pretty well. If the battery level indicator is not a major concern, then the eGo-C Twist is a better choice, if variable voltage is desired.