Battery life.

[Stephen Furley]

Does anybody have any idea how much 'Talk time' a local battery magneto set is likely to give from two 'D' size cells (modern alkaline ones, not the original zinc carbon type)?

[Owain]

Alkaline D cell is about 18,000 mAh

Assuming a 100 mA local transmitter current that would give you 180 hours talk time.

Depending on the load/current curve of the cell, of course.

[GG]

I'd suggest using a set of rechargeable batteries for each phone, and keeping a spare set around that can be charged up and swapped in whenever needed.   

Non rechargeable batteries always seem to go dead at the most inconvenient moments.  For example you have a magneto intercom system throughout the house, and someone is sick in bed and has to rely on it to call family members when s/he needs something.  That's a heavier usage period, and not a good time for batteries to go dead.