I agree with Voyager, and usually when I work on home computers with over 5 years on them I just replace the battery. Its just cheap and easy insurance.
If you're going to change the battery, go ahead and clean out the crud (dust, dirt, etc...) at the same time. Also do a quick check the hardware, is there any cracking insulation on cables, check cable/board connections to be sure they are all still seated securely, do you see any corrosion or burnt areas on the boards, look for any unusual discoloration of parts, and so forth. I do those kind of quick checks of the hardware when I open any computer (regardless of age) as just preventive maintenance.