Vostro 1500 battery light issue?

So the light keeps flashing red and ble and red and blue?. It says in the manual its because it is overheating but i just turned the laptop on shouldnt be the problem. I took the battery out and it stopped turning red. What is the problem? Is it time to buy another battery??Thanks.

 

Usually this means there's something wrong with the battery... or that the machine *thinks* there's something wrong with the battery; I've seen a couple working batteries flash for apparently no reason as well. Does your battery charge/discharge properly? How long does it last?