What is the problem if the battery cannot be detected?

This can happen when batteries go bad.
If the battery is a couple years old you may need to replace it.
There are usually some cheap ones on eBay. The ones you buy from Dell will cost more but you'll get better quality.

Did you buy a replacement battery? Usually this will be because the battery is not an OEM part (made by Dell), your laptop can detect this and will give you a warning. I would always recommend using OEM parts as you don't know the quality of replacement parts and will void your warranty with Dell.
However, if it works, then you may well be ok to carry on.

If this has suddenly just developed from an original part then you have a faulty battery on your hands most likely and I would recommend replacing it.

If your battery will not charge, you need to run a test on some components on the laptop. The battery, the charger and the laptop itself. Once you detect the faulty conponent then you replace it with a new one.

To test the battery:
1.Power off the laptop,
2.Take out the battery,
3.Insert it in another laptop,
4.Check of it will charge,

If the battery holds a charge there, then it means the problem is not from the battery, but if it does not hold a charge, then it means the battery is defective and need to be replaced with a new one.

To test the charger:
1.Unplug the charger from the present laptop,
2.Connect it to another laptop to see if it will charge.

If it charges the laptop, then it means the charger is alright, and if it does not charge the laptop, then it means the charger is bad and need to be replaced.

To test the laptop:
1.Turn off the laptop,
2.Disconnect your present charger,
3.Remove your present battery pack,
4.Insert a well tested battery into the laptop,
5.Connect a well tested charger to the laptop.

If it powers on, then it and charges, then it means the laptop is working fine, but if it does not charge, then it means the connection port of the laptop is bad.Hope this information was helpful.

Dell XPS 15 AC Adapter Charger

There is most likely a problem with the battery. If the charge/recharge cycle very quickly, some of the battery cells are probably damaged. Look for a replacement battery and that should fix it.

See the Adoptor status in the bios, if it is not detecting it the adoptor fault otherwise you have mentioned above you have already replaced the battery then it is m/b issue

-check the system battery information and charger information of the computer; restart the computer, while the computer is booting up, press F2 repeatedly; check "battery info"
-if it stated ac adapter = unknown device ; update the BIOS (-visit support.dell.com
-click on drivers and downloads
-click or choose by service tag
-download the BIOS and install it on the computer)
-check information after updating; if same message AC adapter = unknown device; call manufaturer for a replacement AC adapter, if status has changed it is a battery problem or motherboard, contact manufacturer to test battery

You have run into the same problem that a lot of us with Dell laptops find out the hard way. Yes in fact there is a small chip inside the charging system that will ensure that you will keep getting that message for as long as you try to use a non-Dell battery. As a matter of fact that same chip causes a lot of grief when it suddenly burns out and you start having problems with real Dell batteries. My advice would be to take the battery back ASAP. It does leave you stuck with Dell batteries and prices unfortunately.

Generally, if the AC adapter for the system's LED goes out when connected to the system, check the battery and see if it is holding a a charge (Press the button next to the LEDs on the battery see if all 5 light up)  If the battery still has power, then most likely there is a failure of the motherboard.
If you can, try another Dell D-series AC adapter and see if the same thing occurs.  If the system powers on, replace the AC adapter, if not it is a motherboard.

If the battery is not detected in the BIOS (F2 at boot) and doesn't show as charging, then return the battery and get a replacement.

If neither the original battery or the new replacement battery are not detected in the bios a problem with the motherboard may exist. If still under warranty, contact Dell Support for a repair, if not, then you may be investing in a new motherboard

Try entering the system setup at startup, usually pressing the Delete or F2 key, it may also indicate whick key to press. Once in the setup look for a battery utility. Running the utility, if there is one, will calibrate the battery.