Citroen C6. Dead as a doorstop!

[fastandfurryous]

Hello all. Been a long time since I used this forum, but this would seem a good time to start again... because:

Citroen C6. A nothing-special 1007 2.7hdi.

Currently away from home, went to start it after a few days, and it was in economy mode (no surprise). Dashboard came to life, turned the key and it just barely attempted to crank. "ooh, that's a bit flat" thinks I. Give it a moment then tried again.
Dash lit up again, turned the key, and it cranked for a brief moment, and then everything (and I do mean everything) went dead. No dash, no interior lights, no nothing.
Tried a jump pack on the battery repeater terminal under the bonnet, and still absolutely nothing dead as a dodo. The windows don't jump up or down on door opening, and I can't open the boot as it has an electronic release.
I think the pyro fuse or something similarly significant has failed, as the entire car, every single possible function, is dead. So, a couple of questions for anyone in the know:
Is there a boot emergency mechanical release? This would be good as my work laptop is in there and I kinda need it for work tomorrow.
Is there a pyro fuse on the battery (I am guessing yes, it's new enough for one)
Has anyone any other thoughts?
Any and all useful advice is welcomed!

[mickthemaverick]

I am not familiar with the C6, does it not have a 'Ski hatch' through the rear seat armrest? If so you should be able to rescue your laptop through there!!

[PaulC5]

If the back seat folds down you should be able to get in the boot and poke a screwdriver in a small hole in the lock to undo the boot. There should be something in the handbook about this.

Check the battery voltage before doing anything to see if it is flat, then fuses/links/connections.

[wheeler]

I’ve never seen a Citroen with a pyro fuse on the battery.
Be very careful when closing the doors with a dead battery, there is a risk of shattering the door glass as the glass wont have dropped down to clear the door seal.
I would connect another car with jump leads & leave it running for at least 10 minutes then see if the central locking will work to open the boot.
Did your jump pack have a good connection and is it a high enough output for this car? The under bonnet jump points can oxidise. Could be a good idea to clean them with emery paper

[PaulC5]

I had a jump pack and it did not have enough power to turn a 2.2 hdi we had. Inside it was just a tiny 12 volt battery, pretty useless.

[ekjdm14]

Not sure if this would work on a "modern" car but one trick to get into a locked boot that worked for me on an old E34 beemer that had a dead battery & lock barrel didn't work on the boot.

The car in question had a tow bar with 12S caravan plug, IIRC we jumped a running car to the supply and earth pins for the caravan in order to get enough juice to unlock the boot and change the battery. Either that or as you have access to the interior still you could backfeed through the lighter socket.

I'd have to imagine there's some kind of emergency access to the boot though as it's electronic, probably a case of crawling into the boot and fiddling with the lock.

[PaulC5]

I used to charge the battery on our C5 through the tow bar socket. I had a Lidl charger, cut off the crocodile clips and fit a 13 pin plug to it.