Did some testing with a 1041 seeing how easy it would be to hack it into a 1241 with only a couple inexpensive parts.
The internal mains AC->DC power supply is labeled as 5VDC@2A. Actual power consumption measured by feeding in 5VDC from bench supply directly into the output pins of the built in one (not removing it from circuit) are as follows with screen brightness at 25%
Standby: 6.15mA
Boot: 160mA
Run (VDC mode): 100mA
I didn't test any other modes
The mains ground pin is connected all the way through on the negative power rail up until it connects to the meter board at which point it is isolated from the front inputs.
It seems a bypass switch (/ hard power off), a USB>LiIon>500ma(to 2A) charge+inverter board and a decent 18650 should be enough to keep it powered for about 10 hours for little cost and lots of room to put it in the back with the mains board removed.
Update: I finally hacked mine, and found out it doesn't need a full 5VDC into the logic board. It gets by just fine with direct LiIon 3.x volt output and doesn't need to be boost converted back up to 5V as per the original AC>DC converter in it.
I used a tiny micro usb battery charger and a 18650 cell and connected that up to the AC>DC board, then feeding its second output (that is always kept at the voltage of the LiIon charge when on battery alone or ~4.2V when connected to a 5V input.
To my surprise it has been running fine at the lower voltage without issues. I presume it may be dropping to 3.3V or so anyway once on the logic board, but didn't go poking around to verify.
I thought I'd share for anyone else that wants to do a quick hack of the AC powered one into a 18650 powered version. Just need a couple 5 pin male XH2.54 male header pins and a 5 pin female plug with just 2 wires for voltage and you can bypass the feed through to the serial port then and connect up the battery/charge chip.
I didn't take a picture of my mod, but here is a quick drawing.
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