Dell XPS 1340 battery not charging Charger and battery seem OK

I have a dell XPs 13 (1340) which is about 4 years old.

The battery was getting old and finally losing charge under 2 hours.

All of a sudden the battery stopped charging.

1. I have 3 chargers, one that came with dell laptop, another one is also a dell that came with a different dell laptop and a third generic one. All three used to work fine and they still work fine with my other dell. But can not charge this laptop battery. So charger should not be a problem.

2. The battery icon shows as blinking red X and not charging symbol and stays at 7%. When I go to battery meter it shows discharging. I first suspected as battery being dead and ordered another battery. Thought it was original dell on Amazon but the seller sent a generic one. When I installed that battery, it shows as 7% and does not charge either. I can briefly disconnect and move to a different place and connect back and I do not lose any info.

3. When I powered by removing the battery, it complained saying no battery installed.

So based on #2 & 3 above it looks like the battery is recognized in the laptop.

4. While the laptop is connected to power supply, it still works fine. So the charger connection should be OK.

5. When I looked in BIOS, it shows NONE as power adapter. So this is confusing.

6. Today, while working on the laptop the charger must have accidentally disconnected and after few minutes laptop suddenly shutdown. When I powered back up with charger, the battery now shows 0%. So I must have used up the 5% on one of the batteries.

What could be the problem? What else I can try? Based on my above testing I do not suspect battery, power charger or connections.

Thanks