This is what I would expect! I think what marinheiro is doing is applying the "post hoc, ergo propter hoc" reasoning. The battery just happened to deteriorate naturally.

@marinheiro, if you want to make sure the N900 doesn't waste cycles looking for a connection, you should install Cellular Modem Control Buttons. This very nifty feature will allow you to select "Tablet Mode" from the Power Menu. That mode disables the cellular modem. I use it on my own N900 when I don't want to receive calls and Silent mode won't do. All "repurposed" N900s not used as a phone anymore should be set to Tablet Mode.