V70 with flat battery doesn't start anymore

[rtartari]

My gf left the lights on, my beloved V70 D5 from 2009 is dead. The brake pedal is hard. I attached another car battery red on red and black on my volvo's frame. The starter motor turned but the engine didn't start. Could it be the immobilizer? The car is so dead that I could not lock it with the remote so I had to manually lock the doors and use the key inside the remote to open and close the driver door. Any suggestion how to bring it back to life?
Thank you!

Riccardo

[BorderVolvo]

Assuming the remote now works again, I would use it to lock and then unlock the doors......hopefully this will reset the immobiliser.
After doing this try cranking.

[xavierx]

Originally Posted by rtartari

I attached another car battery red on red and black on my volvo's frame.

I have seen this exact same problem when I was restoring a xc70.

I added a second battery by jump leads and the car would not start.
This seems to be because some modules go into a permanent sleep state after a low voltage event.

You need to fully disconnect power to the car and then re-connect to wake everything up, so disconnect the original battery

[Tannaton]

Combining both of the above, remove the battery and fully recharge it (or replace it), reconnect and then lock the car on the remote, then unlock it and then go for a start…..

If the car was locked on the remote before the battery discharged, may still be immobilised.

[rtartari]

PROBLEM SOLVED! I disconnected the battery, waited a couple of minutes, reconnected everything and attached the donor battery red on red and black on black, waited another couple of minutes, closed and reopened the car and it started perfectly fine. Thank you to everyone who posted... Definitely a good lesson learnt.

Best,
R