I'm having a problem with my laptop and I'm trying to pin down just exactly what is wrong. When the battery is in, the charging light will turn red and the laptop will give me power warnings. I jiggle the power cord and the light goes back to yellow, as if charging. Ok, I think it's the power cord. However, the second light, the incoming power light, always stays green. So I remove the battery and everything is fine. So, is my battery dead? Would that make my laptop shut down, even though power is coming in through the power cord?

2 problems... and this is quite common. The contacts in the power jack become weak and loose, which adds resistance and therefore limits the current flow. (very common problem with laptops) The power is still ther but not in strengh. The battery then kicks in to make up the difference under the heavier loads, and as a result, dies prematurely due to all of the "mini cahrges and discharges". When a battery goes it will either start pulling a large amount of current because of the internal shorts, or it will show 100% charge and last only a few minutes when in use. The first example being your case. At some point it will start pulling more current then is available which will cause your computer to start firing off wraning bells, and in extreme cases, it will simply shut down. It is not enough to simply replace the battery... you will also have to open the laptop, clean and refit the power jack. However if you are a bit lazy like me, you can simply pull the power cord tight and tape it to the back of the laptop. This puts enough pressure on the contacts within the jack, so that current flow is restored.... but get rid of the battery... it's naow quite literally a drag on the computer.

Add to the above, that at least in the case of Thinkpads, there is a fair amount of circuitry RIGHT IN THE BATTERY housing, which can develop problems just like any other electronic device. Loose power connector Intermittent power cord (usually right at the connector) Bad/ going bad battery Broken/ bent/ loose connectors from laptop to battery. Sometimes these problems simply can't be fixed by the average joe or judy.