Vax Blade 3 not working

I have a blade 3 Vax cordless vacuum that no linger works as it should. The battery pack (18v) does not recharge on the charger

The individual cells are showing about 3.7 volts each and the motor runs for a few seconds before a "code red".

I suspect the battery managment system is faulty.

What I would like to do is "convert it to corded" i.e run it off an adaptor. The motor rating is 160 watts at 18 volts, and the charger adaptor is 18 v at 1.5 watts.

So is the 160 watt motor rating the no load, load or stall amount?

Does it really need a 9 amp rated 18 volt adaptor? (160 /18)?