Hi Paul,
Yes, that battery would work, though it would not be optimum as it is not a deep-cycle battery.? Walmart does make a U1-AGM battery that is designed for the type of operation that you describe.
The length of time that the battery will power a QRP rig will depend on the rig and operating practice.
I would assume a 5-watt transceiver with 100MA draws on receive.? I would also take the worst case of 25% efficiency of the transmitter and 50% of the time transmitting.? These are very much the worst case.? I would also assume that the average voltage supplied by the battery is (voltage fully charged + voltage to discharge point)/2 or (13.5+12)/2=12.75 volts.? NOTE: most batteries are not recommended to discharge below 12 volts.? Also that the maximum voltage is not 12 volts.
With the above assumptions, the average current draw during transmission would be I=P/(V*.5) or 5/(12.75*.25) = 1.57 amps.? NOTE:? efficiency of the transmitter can have a significant effect on the run time for the battery.? Substitute the current draw when transmitting for your rig.? Most of the QRP-Labs transceivers use less than 1 amp on transmit.
The average current draw per hour would be (1.57+0.1)/2 = 0.83 amps.
The battery is listed as a 35amphour, so approximately 35/.83 = 42 hours.
Above are my best guess.
73
Evan
AC9TU
