Inspiron 1150 battery light flashing in spite of full power

I bought this Inspiron 1150 laptop in 2004. The battery power can only
last about 30 minutes. Recently I used it on battery till it
completely ran out of power. The next day I plugged power cord in and
used it normally, charging battery to its full capacity. But there's a
problem. The yellow light at the front keeps flashing as if my power
was running out. How can I tell it my power is already fully charged?
If I unplug the power cord now, I can see the blue cylinder power icon
showing 100% full.

 

Flashing light means that the battery isn't charging correctly, and being 6
years old, probably is on its last legs. It is reporting as full even
though it probably isn't. If you would try to run on battery power alone,
you probably won't get more than 10 minutes, as the cells are not charging
correctly.

 

Thanks John. That makes sense. I'll think about whether to replace
this laptop or just the battery.