The batteries on laptops are often a problem. Most people sit their laptop on a desk and use AC power, so the battery usually suffers, resulting in a chemical 'memory', which gives them a life of about 3 seconds under load. The batteries in my donor laptops were both made in 2000, so I had to try and revive them. If you have any NiCd or NiMH batteries that won't hold their charge, you can often revive them. This is not a new concept, but here is my recipe for reviving rechargeable batteries:
- Discharge the battery as much as you can.
- Place in a sealed plastic bag.
- Place the bag in your freezer for at least 24hours. Overnight is sometimes enough, but I leave it about a week.
- Take the bag out of the freezer and leave the battery to return to room temperature. Make sure you wipe off any condensation from the battery contacts before you use it. I just leave them in the sun for a few hours.
- Fully charge the battery, then run it down again, as low as you can get it. Repeat this charge-discharge cycle a few times, and see if you get a longer life.
Your mileage will vary, but two of my 5-year-old batteries are now useful. I get between 2 and 4 hours from one of them, depending on the load on my laptop. You can do this with cellphone batteries, or batteries from lots of other gear.
(courtesy: a freak geek who just ressurects absolutely anything, which is portable)