T440 continues brinking green 3 times, pause, and brinking 3 times 3

[torpl]

Days ago, I forgot to shut down my T440 when left home, and left it ran under battery mode (no AC plugged in) at 100% charged. When I was back after a few hours, of course the T440 was powered down (or hibenated) at low battery. I powered it on and it did start running, but auto power off within 3-4 seconds. Most of the time it shuts down after BIOS stage completed and just when it entered Windows 10 and the blue win10 squares was shown. Sometimes auto shut down during BIOS. So indefinitely but all less than 5 seconds.

I observed that when the the T440 is off, and AC connected, the power light keeps blinking green 3 times, pauses, and blinks 3 again, continuously. I have tried all the methods suggested in the Web like remove cmos battery, reset thru pin hole, press power button 30 seconds...etc. All did not fixed the problem.

HOWEVER :
1. When both the internal and external batteries of T440 are removed, yes it has two batteries, the machine WILL RUN PERFECTLY fine under AC power only.
2. If after 1 above, I plug the external battery in, the windows battery indicator will shows charging battery for 1 second and the machine then auto power down. Just like as if plugging in the battery will "drag" the system down to shut off.

I have tried changed to a more powerful 90W charger (all Lenovo made), but same.

Simply speaking, it runs well under AC only. But with AC + battery attached, it did powers on and boot, but auto shuts down within a few seconds.

The charging port on the machine (not the battery) the middle 3 pins also each gives out 3.4-3.6 volts for charging the battery if measured by a meter. Do it means the charging circuit/port is okay?

Anyone has suggestion why, and how to fix? Thanks.

[axur-delmeria]

The T440 has two batteries right? Try disconnecting or removing the internal one.

[torpl]

Thanks axur-delmeria,
I have tried removed the internal battery already. See my point 1. in above, towards the middle of the paragraphs. The T440 only works under AC with BOTH internal and external batteries removed. If either one or both batteries are connected (with AC power of course) it will power on and boot for about 5 seconds and auto power-off.

[RealBlackStuff]

Borrow some (working) batteries from another T440, to see if your laptop is otherwise still OK.
Or try your batteries in another T440.