Wondered how long you could run your BGW210 on an external battery backup power supply? The answer is quite a long time--it draws only12 Watts while on and transmitting wi-fi.
I measured this draw at the 110V input to its EPS36R0-16 adapter supply (which is rated much higher at about 36 Watts).
The measurement was made using the power meter built into my Generac GB1000 uninterruptible power supply.
FYI--When the BGW210 is also producing the dialtone on a connected landline, it draws one additional Watt.