Recently I had to replacement the battery in my Garmin Nuvi 750 GPS unit. I found this web site that has a lot of videos on how to replace the batteries in all types of electronic devices.
http://www.newpower99.com/ they will take you through the process of opening the unit and making the replacement.
I just used the video as a guide and went to my local Battery + store and purchased the battery there. The closest store to TV is is Ocala. When I was in the store I mentioned that I would order it on line as Newpower99 would include any tools needed to open the case the sales person said that he would give me the very small torx screw driver free as they so many of them they just toss them away. I guess they get a new one with every dozen batteries that come in.
I have not dealt with Newpower99 but am posting this a link to their videos.