I have had a Garmin 205 for almost 4 years. The battery is still fine (8h). So maybe you shouldn't worry. However I do know that Garmin do a replacement programme for a fee, which is not unreasonable
You could try Royles in t he centre of Wilmslow (Grove St). They have a good selection of shoes and video gait analysis. Worth a look at their website www.royles.biz before you go as they have sale shoes that they can get to the shop if you ask beforehand.
Try searching for Leek half marathon route on google.There is a profile in mapmyrun. Basically 0-11.5km uphill then downhill to the end! Not easy I think but I will be there!