--------------------------------------------------------------------------------
So Jeff1, what's going on, don't varistreams like flat batteries?
Nothing we have likes a flat battery, were all inclined to think that a flat battery is something with all the power drained from it, where in reality a battery at or below 11.2 volts is considered to be flat.
All electrical items do have a +/- of a few volts and unless a piece of equipment is built from top quality components, then this tolerance factor of +/- can vary quite considerably, so where your varistream may stop functioning correctly at 11v mine might not stop until the voltage was around 10v or vise versa.
Also don't forget that if your battery is not fully charged each day, then more and more problems with your electronic equipment will raise its head more and more each day.
Like always my advice is fully charge your batteries on a regular basis.