I have a Dell ML3109. It was the cheapest laptop that Best Buy had when my wife bought it for my birthday 18 months ago. The battery is not charging when I plug it in. A month after I got it, I broke the charging cable and bought a replacement. The cord worked fine except that the battery was not charging. I found after a while that I could force it to charge by unplugging it and plugging it back in (by separating the parts of the cord and leaving the end plugged into the laptop). So, it’s misbehaving in the same fashion now, but that trick does not work. Does this mean the battery is toast? I’m up for suggestions. I don’t really use battery power that frequently, but it’s noce to be able to unplug it and move around the house with it. And now I can’t do that! 
The part that the cord plugs into inside the laptop motherboard itself likely has broken off from the motherboard.
Here’s a site that talks about what I mean. I’ve successfully repaired my own but it’s a PITA if you’re not used to soldering. (Which I’m not, and I burned my nose in the process.) The part is cheap cheap.
If you bought the laptop 18 months ago, it’s probably still under warranty (unless the battery is the problem as they are usually only covered for 1 year). If you can live without it for a few weeks, that’s probably the best route.
You can use the following website to find out: Support | Dell US
I would only go with Rasa’s suggestion if you knew it was out of warranty (or you were unable to live without the laptop).
Did you get a Dell-branded replacement cord or a generic one? I have a Dell and the cord broke so I bought a universal one to replace it, but it wouldn’t charge the battery. When I got a Dell cord, it worked just fine and my laptop sped up noticeably. If the replacement is Dell-branded, that is beyond the scope of my experience.
If you have a Best Buy warranty it should cover the battery. I got a new one for my old laptop one day before the three-year warranty expired. It was a cheap replacement, but I got another year out of the replacement battery.
Thanks for the replies. It’s actually a Gateway computer, oops, brain fart. It just suddenly in the last couple weeks quit charging and I bought the generic replacement cord a few weeks after we got it.
Can Best Buy test the battery?
On my computer, the battery sometimes does that.
I don’t usually let it run on battery for very long because the battery is crap and only lasts like an hour anyway, but I do sometimes unplug it to move it without turning it off. For a while it would lose a little charge every time it was unplugged, but once I plugged it in it mostly stayed the same. (this is all for reference to see if it sounds like your problem, not just because I like to talk about myself)
Anyway, my computer told me that I’m supposed to let the battery run out completely, like less than 2 or 3 percent, and then turn it off and let it charge. That usually works. The one time it didn’t work, I took my battery out and blew on it (because that fixes everything.) and then put it back in and it charged just fine.
If that doesn’t help, my next step is usually to make frustrated gestures at it and go, “why don’t you ever work, you stupid piece of obsolete crap?!” and then roll my eyes and flop dramatically in my seat. That method has a pretty high failure rate, though.
You should be able to check the battery connectivity and health in the BIOS. I know it’s possible on a Dell, so presumably it is on other systems, too.