M6600 plugged in/won't charge

Hi,

I'm trying to troubleshoot a used M6600 running Windows 10 with a battery that isn't charging (original battery and charger). When I plug the laptop to the wall (in either on/off states) the battery charge indicator flashes​ momentarily and then gone. I get the same result in different sockets.While plugged in Windows battery status indicator shows "plugged in/not charging". The battery doesn't charge when the laptop is left plugged in overnight while off​, nor does it stat charging if I insert it into an already running session.

I took several steps attempting to solve the problem, checking after each step before advancing. 

1. Updated to the latest BIOS from Dells website. It didn't solve the charging problem but enabling messages from diagnostics gets a message at Post notifying that the AC adapter isn't adequate for the laptop :"Alert! a xxxxxW AC power adapter has been detected, which is less the the recommended xxxxxW AC adapter originally shipped..."​

2. Unplugging the laptop, removing the battery, uninstalling both ACPI drivers and replacing the battery.(However at this point it became apparent that hardware is the source of the problem rather than Windows since the battery won't charge while the laptop is turned off while still plugged in).

3. Unplugging the laptop, removing the battery and pressing down the power button for 30 seconds in order to clear the CMOS, then plugging in and checking.

​4. Blew both onto the charger's plug and laptop's plug receptacle in order to remove dust.

5. Cleaned the battery contacts with a dry cloth.

How can I be sure whether it's the battery or charger at fault? Is the charger adequate for this laptop to begin with (65W 19.5V-3.34A AC adapter [model #LA65NS0-00])?