Hi, I'm new here and I hope I can find a solution to a most puzzling problem.

I fix laptops for a living and I was recently given a N56VJ which refused to power up. I concluded that the motherboard was dead, so I organised a replacement identical model. Also, I got a new charger and battery as I needed these for future jobs and I thought they'd be good to use when the new motherboard arrived.

Once I got the new motherboard, I installed it and it worked quite happily. But one thing I noticed was that the battery wasn't charging. Before it came to me, this laptop had done the rounds of several other computer repair companies, none of whom had managed to get it working. During that time, it seems the battery was left discharged so I assumed it was now useless because of this. So I tried the new battery and still nothing happened. It arrived 60% charged but it just lost charge even with the charger plugged in.

So, after a lot of messing about, including a re-installation of the OS (Windows 8) on Asus' technical support advice, I have this odd situation:

1. If I leave the battery out altogether, I start it and it runs fine on A/C power.
2. If I plug the battery in and try and start it, it won't. If I check the charger voltage, it often reads about 8-9V, instead of around 19.5V. Even if I disconnect the plug from the mains, check the voltage (now 19.5V), if I plug the charger in, still it won't start. I know I'm not supposed to plug the charger into the laptop first but I had to try all combinations.
3. If it's running on A/C, and I plug in the battery, the amber charging light comes on, the battery charging icon animates for about 15 seconds and then stops. The percentage charged figure stays the same. If I use a battery monitor, it says only 30 to 100mW are going into the battery which is way too low.

I've run out of ideas on this one. With a replacement motherboard, charger and battery, I can't think of anything else to change! The RAM seems ok, although I haven't run Memtest on it. The HDD checks out ok.

I find it hard to accept that this replacement motherboard has become defective. Besides, I measured the voltage on it's pins,it was about 2.8V. I have rigged up the old motherboard which still has usable charging circuits to charge the battery. I have even flashed the BIOS, there is no update for it available.

I would appreciate any advice on this one as it's driving me nuts! Many thanks.