If you want to have a go at replacing the battery yourself, replacements can be sourced here:
http://www.espspecialbatteries.co.uk...%20TRANSPONDER
other vendors may be available.
You can use someone to do the replacement for you, and pay that extra, but if you take your time it is achievable by most people, just be carefull.
Remember that if you open it yourself wave goodbye to any warranty.
Regarding PT's, I think if we do go down this root, there has to be some responsibility from race control to advise of poor signals, perhaps during practice. Usual problem I see is pt plugged in reverse into Rx, shows up on bbk software as an usually thin line in the signal strength monitor.
Also as another option to what has been discussed above, you could purchase 1 of the new AMB rc4 pt's, and an extra cradle for less than £2. This then allows you to slide the pt out from one car and into another. Just an idea to consider.