2007 XK flat battery

I have a 2007 XK coupe that rests for the winter, with trickle charger connected. When I went to start it today, the doors would not unlock, so I used the key. No luck. The car does not respond to any of the buttons on the remote fob, even with a new battery. Everything worked a month ago when I last started it, so I am now assuming that the car battery is dead. I thought that the key worked like any other key, but it will not open any of the doors, so I am assuming again that it just operates the electrical switch, so no battery power, no open sesame!
So, in short, how do I gain entry into the car if the battery is dead?

Have you tried the tailgate keyhole which is behind the rear numberplate?
If that won’t open with your key then you can connect a jumper battery to the car from the outside.
First look under the rear bumper behind the passenger (UK) side rear wheel, look directly up at the vehicle floor. You will find the main battery cable attached to a stud, pull back the rubber cover and attach your positive jumper lead to the stud. Next, attach your negative jumper lead to a good ground under the rear floor, clean the metal if necessary. Next, attach the other end of your positive jumper lead to the positive terminal of the charged battery and finaly the negative jumper to the negative terminal of the charged battery.
Make shure that the charged battery is not in contact with the vehicle.
You should now be able to use the fob to unlock the door, once you have started the car, leave it running for a few moments before you disconnect the jumpers. Always connect negative last and disconnect negative first to avoid electrical spikes.
If you are connecting the jumpers to a battery which is installed in a vehicle, do not disconnect while the doner vehicle is running as this will cause damage the your vehicle electrics.
There is a procedure to follow to reset the adaptations after replacing a discharged battery, I will look it up and add it to this topic.

I have not been able to add the PDF, so I will type it out.
1, Start the engine and allow to idle until the engine reaches normal operating temperature.
2, Switch off and restart the engine and allow to idle for two minutes ( this will allow the ECM to learn the idle values.
3, Apply and hold the brake pedle, select drive and allow to idle for a further two minutes.
4, Drive the vehicle for approximately five miles of varied driving to enable the ECM to complete it’s learning strategy.
5, Reset the radio and windows.
I hope this helps.
Regards, Dave.

Thanks Dave, I will let you know how I make out.

Hi Dave, that battery post was just where you said it would be (even on my LHD) so I was able to open the hatch and now have the battery on charge.
Thanks again for your help.
Regards, Mike

Hi Dave, it seems that the trickle charger failed and completely drained the battery, and I couldn’t charge the battery until I disconnected the trickle (permanently connected to save removing the panel)
Now I am getting codes P0001 and U0001 which google tells me are communication problems, and a restricted performance message, even though performance seems normal. I cleared the codes but they return. Do you have any ideas how to get rid?