At the risk of appearing stupid, I must confess that, even though I've owned various laptops for several years, nobody ever told me that it's very bad to leave your laptop plugged into the AC charger all the time, with the battery inserted.
I had bought a new battery when I got my most-recent used laptop, and was frustrated when, a year later, it would never charge more than 4%, and always appeared to be on the verge of running out. Likewise the battery in Karen's laptop (again, always plugged into the AC), which also, should you unplug the power cord, showed little juice remaining.
I recently did some googling on laptop batteries and charging problems, and came across a site that offered a suggestion for laptop batteries that appear to be virtually dead and unable to recharge. It seemed preposterous.
1) Remove battery from laptop.
2) Slip it inside a ziplock plastic bag.
3) Wrap a dishtowel around it and place in your freezer for at least 13 hours.
4) Remove from freezer and let it slowly come up to room temperature.
5) Insert battery back into laptop, plug in the AC cord, and power up.
6) Go to 'Control Panel | Power Options | Power Meter' and prepare for a shock.
My battery, which never showed more than 4% charged (9 minutes remaining), immediately showed 97% charged, and charging.
I let it sit for a while and when I looked back, it was up to 98% charged!
I unplugged the AC and the control panel updated, to inform me that 'Total time remaining' is now 3.57 hours.