battery indicator

Darwin, a possible cause is that your battery is too hot, and as a safety measure, your laptop will not charge it. Try turning off and unplugging your laptop and letting them cool down to room temperature, and then the problem should disappear for a while.

For the long term, the next time it happens, put your hand on the battery case. If it is hot, your battery might have an internal leak and could ignite or even explode. In that case you need to turn off your laptop immediately, unplug it, leave the area, and when it is cool get it replaced.

I also recommend downloading the free Core Temp program. It won't check your battery, but it will tell you if your machine is too hot. A careful shot of compressed air into the exit vent could help.

Incidentally, everything I found on the subject says that you need to replace your battery. At the very least, it is failing, as all batteries eventually do.