MacBook won't boot after shut down without SMC reset - Every time.

I've been asked to look at a friends Late 2011 Macbook Pro.

Initially it seemed dead. No power, no response. I did the Shift+Comman+Control+Power to try and reset the SMC to no avail.

I opened the back and disconnected the battery and magsafe. I help the power button down for 5 seconds. reconnected the batter tried a power on and it didn't work until I plugged the magsafe in. Ah ha I thought, BUT. Once booted it works fine, did some checks all seems good and battery shows as good health with 70% charge.

I restart the machine and it boots fine. HOWEVER. I shut the machine down and I'm back at square one. Power supply still in and battery connected.

So I rinse and repeat. battery unplug power out hold button wait 5 plug all back in and then power on. Like before it only powered on once the power supply was ALSO connected. to test this I tried it again without plugging the battery in and just the power supply. Like when only the battery was in, nothing happened until I ALSO connected the battery.

So the Macbook will only boot after a shutdown if the battery and power are BOTH removed, the power button help for 5 then BOTH the power and battery are plugged back in.

I've seen people with similar issues but nobody seem to list the specific symptoms that it requires this reset every SHUTDOWN but not on restarts.

Any clues, helps, fixes?

Cheers

Paul