Using wall wart as 9v Battery Backup

I have a CO/Natural Gas meter that requires a backup battery to be able to function (without beeping), even if it is plugged in. I find that I am replacing batteries every couple of months (I have 4 in my house). I am wondering if I can use a wall wart for the 9v supply. I know that the 'backup in case of power failure' function would no longer be present, but that is not a concern of mine.

Better yet, can I hook up the 9v supply that comes with the unit (9v 400mA) to the 9v battery connector, so that the supplied 9v adaptor effectively runs both the unit's main power and it's backup? I have opened up the unit and the soldering would be incredibly easy.

Thanks in advance for any options that may be forthcoming.

• Please provide details of the "meter" (or do you mean "monitor"?). – Andy aka Nov 28 '16 at 15:18
• This is the monitor: homedepot.ca/en/home/… – Fed Nov 28 '16 at 16:04

Not knowing the circuit sensitivity to overvoltage and knowing wallwarts will be unregulated at 50% higher voltage with no load, 40% from rectified rms and 10% for DCR loss in transformer at full load, you can certainly choose your own appropriate supply if you understand the risk of overvoltage and need for reasonable regulation 10%.

Why do you have 4 gas meters? You mean Carbon Monoxide smoke alarms. How many hours of power loss per 2 month? You could run a 9 V LDO at each meter from a 12V SLA and feed from spare wires in telephone jack if only using 1 line. The monitors may need low ripple so measure both Dc and AC V to ensure proper performance with self test.

Another battery solution is 9 V Lithium which last 2-3 years or more from online sources. $10 approx. or use 3x CR123A Lithium in series @$1 each in bulk online.