Macbook only works without battery

As far as I can tell, my 2-year-old macbook is working fine when attached to power with the battery removed. But as soon as I put in the battery, the computer immediately goes into sleep mode. It will wake up for about 3 seconds at a time, then it goes back to sleep. As soon as I take the battery out, it comes back to life and works fine.

I tried resetting the PMU, no change. Any idea what's going on?

Have you tried asking a friend or colleague or what ever to borrow their battery and test it out. It would be a great test before you go out and spend some money on having it fixed.

I'm having the same issue! My macbook works fine if i disconnect battery during boot. (otherwise it will sleep after 3 seconds) i did spill a small amount of wine on the shell, and stupidly started it right away thinking that I hadn't done any damage. worked ok until the next day. am also wondering if this could possibly be just a battery issue or have i done internal damage?

it could be a battery issue. The system will reduce processor power when the battery is not plugged in to ensure that the system does not draw too much power. When it senses the battery is plugged in this is not the case. If the battery is bad, you could pull more power than the battery and power supply can provide.