55v on one blade and 55 on the other is 110VAC, which is very normal for a US home. Not out of the ordinary at all. To see this, put the black lead in one and the red lead in the other...not ground as that's for checking DC. What's the "Good" voltages you get right from the plug?
one blade (neutral) should be zero to ground, the other (hot) have some sort of voltage to ground. hot/neutral/ground. the 55v may be because of the stepped square wave output (that the cheaper UPS use) on a voltage meters AC scale that expects a real sine wave.
maybe youre thinking 240v lines with two hot legs (120+120+neutral)?
but yea the smaller APCs just pass AC from the wall on. they dont kick in till theres a problem
By saying you need UPS units in the backwoods has me seriously thinking there's something going on on your end or you just wouldn't need 9 units to keep things powered.
Im in the sticks too. our power is The Suck. I have 3 APC UPSs they kick in a few times a week, and they are all set to "low" sensitivity and pretty high/low values for high/low voltage triggers or they went off several times a day.. but interestingly enough, the one PC not on a UPS still survives the sags/noise/whatever.. some of them bad enough the lights dim to next to nothing for a second. Antec basiq 500w.. not the best PSU I know but it was a BB gift card special.