If I read that right, are you talking about an uninterruptible power supply? If that's right, aren't those just for giving you a few minutes to turn off your electronics safely in the event of a power outage?
If this is all correct, it seems like you're expecting that to act like a generator or something when it's really just a bunch of batteries designed to save the data on a device like your computer from being lost by continuing to power the device (ex- a computer) for a few minutes so you can save what you need to and shut it down safely if the power goes out. Then since it's using batteries to give you that extra few minutes of power, they'll need to be charged before they can be used again.
If I've misunderstood, please tell me.