Some people might say I own too many phones. Those people are wrong. I've got a small collection of Gai-Tronics phones and recently got one of the speed dial memory ones for £20. It's missing the handset cradle, so it's not quite fully operational.
Before I got around to testing it I saw a post on a forum stating that the memory speed dial versions of these phones tend to die prematurely. Someone else suggested it might be due to a dead battery.
I hooked it up and whilst inbound calls worked fine, sure enough the speed dial button didn't work. Hmm. Time to take it apart.
Taking the thing apart is fairly easy, with 3 bolts holding the front to the rear enclosure. Once inside you can see the main circuit board with the programming keyboard attached, and sure enough, a battery. Its the white cyclinder with the green band on the right side.
Sure enough it was sitting at 0.1V - well below it's 3V rating. To test the theory I snipped it out and hooked it up to a Power Supply putting out 3V. Note the polarity is printed on the circuit board. In my case positive was facing the bottom of the phone, but it might vary between models. Be careful!
Sure enough it worked and I was able to save and recall a speed dial by following the instructions on the programming PCB. To my surprise it still worked after I'd removed the power, but it turns out if the phone line is removed it will forget it's settings again. Evidently the battery is just to maintain the backup /provide planned obscolesence...
The replacement battery is a 3V (Possibly listed as 3.6V) "CR 1/2 AA CR14250 L14250" - I picked one up on EBay for 3V and it should be straigtht forward to solder it in.