Solid red battery led light when ac adapter removed

Hi, I bought my Inspiron 6400 in December 2007 from Dell. I've been taking my laptop battery out when it's connected to the AC adapter to save the battery from charging too many cycles. Not sure if this is a wise thing to do? And is it really bad to take the battery out when the laptop is still on or do you really have to turn it off first?

Anyway, now I seem to have a solid red led light when I take the ac adapter out and it runs on battery. It still seems to run for maybe 10 or 20 mins without the adapter. However, on bios and on the battery meter, it says the battery is not detected. I checked the indicators on the battery and they seem to be green and then when I press for longer, all the lights are still green before they go out. Does that mean my battery is faulty and needs changing? Or is there something with the connectors because I've been taking it in and out so much and that's why my computer isn't detecting it anymore?

When both battery and adaptor are in, there's an occasional flicker of green light in the battery light but nothing constant.

I haven't got a spare dell battery to test what is actually wrong nor do I know anyone with one :-( I would buy one but they're quite expensive so want to make sure that it's actually the battery that is the problem.

I would've thought if the battery was dead, it would still be detected by the computer? But then again, it still seems to run off battery alone..

If anyone has any thoughts, it would be much appreciated! Thank you!