BMW GS 1200 Adventure tire pressure sensor

I finally grew up and sold my super-bike and bought my self a project GS 1200 Adventure 2008 and i finished it about 4 months ago, I have learnt the BMW spares are pretty expensive and when my tire pressure sensors went and i found out that they cost R1400 each (Now that expensive) I got told if i need tips or anything else i need to get on to the Wild dog site, i have spent the day just browsing the site and i was amazed what you can buy sell etc, I am sure i will be able to get some help, as i understand it is only the battery that has gone flat i am sure this can be replaced. Can it be done? and if anybody has done it have you please got some tips for me?