Dell Vostro 3500 is not detecting the battery

"Dell Vostro 3500 battery is not recognized by the laptop and is not charging"
Here are few things to try:
1.Check if the battery works in another laptop.
2.Clean the battery contacts if you’re comfortable with it. Also check if it’s damaged or bent.
3.Try another battery. If this vostro 3500 battery works, then you know for sure that the other dell vostro 3500 laptop battery is faulty. If the system is under warranty you can get battery replacement from Dell.
4.Seems like flashing BIOS has helped a great deal of people facing similar problem. Here is a Knowledge Base article from Dell that has solutions for battery problems. Follow the instruction to get BIOS update.
Hi there, since you tried a "known good" laptop battery (exactly the same as your original one I hope and known to work already in another machine) and the system still didn't recognize it, there really isn't any point in troubleshooting the battery.
If you are able to use your portable on dell AC power adapter without problem, then you can rule out the system itself as being at fault.
Try booting the system into the System Setup (BIOS) and check to ensure that the battery is seen in there. Turn off the system, then turn it back on and tap on the F2 key a couple of times when you see the Dell Splash screen. When you get in there, take a look in the list for battery or power options. See if the battery is being detected by your system.
If it isn't, then that indicates that there may be a fault in the connectors where the Dell 7FJ92 battery plugs into the system. You may need to have your motherboard replaced.
If your system is under warranty, Dell will replace it for free. If not, they will still troubleshoot with you to determine exactly what is faulty or causing the issue, and will point you in the right direction to get it fixed.
Just to check, the new battery is the same kind right as the original one right? If not, you may be getting a false failure as not all batteries work in all systems. "