krousson wrote:

> hello group; a post with 2 linked questions about UPS:
>
> i have a mobile application requiring UPS online supply, for a "small"
> load (approx 250W) that needs to run for 1 hour. more than half of that
> power is drawn by 12VDC equipment.
>
> question A: can i extend a UPS's runtime by simply adding similar
> batteries? in general, what do the chargers know about voltage and
> capacity of the batteries? if there are more batteries, same voltage,
> will it only take more time to charge? (and then, to discharge...)
>
> (safety note: this setup will never run unattended; it powers equipment
> that is constantly monitored)

Look here for a thorough discussion of this:

news:alt.comp.hardware.pc-homebuilt
Using an External Battery for a UPS -- Belkin 1100VA