Hi,
Yup, sounds like you'll have to put it down as one of life's experiences.
Having been in to help "pick up the pieces" many times over the years, I've come to learn very quickly that you should never trust builders or electricians with data or telecomms cabling.
Take a look at the Siemens Gigaset range of wireless phones .... quite nifty and have some good energy saving features on them, for example you can configure them to turn off the radio subsystem when there's nothing happening..... as a result they can hold their charge for an eternity (well, ok, perhaps more like a week based on my non-scientific experiement)