One concern just dawned on me.
I used a SWM3LNB, my concern is powering TV, H21 & PI off a power inverter.
Anyone have any thoughts on this!
... Let's split the difference and say 150 watts.
...a typical deep cycle marine battery rated at about 100 amp-hour
... you could run for about 4 hours on an inverter
I've done a number of tests since the original question and my answer were posted, and just wanted to post a quick update here in case someone searching finds this thread. Using an HR24-500 with an AM21 tuner, and a Samsung 46" LCD TV, which combined have a measured power draw of 205 watts, I got 4 hours powering them off a 400 watt inverter connected to a Sears size 27 marine deep cycle battery (rated 105 amp-hour at 20 hours). There was still some battery power left, and I'm sure I could have gone to at least 4.5 hours, but decided 4 hours was enough for the purposes of this test. The battery was fully charged at start, and measured 11.23 volts (still under load) at the end. It should easily power the system down to 11 volts, which I'm estimating would have given me another 30 minutes.
A similar test using a 1200 watt inverter powering two 100 watt incandescent light bulbs (200 watt load) connected to a similar sized but newer battery, gave me over 4.5 hours with an ending voltage (under load) of 11.29 volts. That inverter was connected to the battery using much larger power cables (less dc voltage loss between battery and inverter). Same battery and inverter gave me well over an hour with a 600 watt load.