It's a bit less than a one-shot disposable battery. Something along the lines of 1.3 V for a fully charged cell. In some high-current devices (such as a "hoverpuck" floating toy") I have noticed a very, very small loss in effectiveness. In most other devices there is no difference at all.
By D. Wick on November 21, 2014
These batteries don't say anything about 9 volts. The Energizer Batteries I purchase have a different label and I am in the process of testing one now. It's mate has held 9 volts since receipt sitting on a shelf. Next week I will see how the other battery is doing.
By Ed L. on February 1, 2013