They sell fleet jumper cables wich bolt directly onto your battery and comes down into a push in plug connector underneath,you take the other part and connect to the donor car battery or car battery you have in trunk as spare from boneyard....push plug together underneath,now both the charging vehicle and dead vehicle are now connected and chargeing as one...press key fob door will open.
Also you can have whats called an all weather push button switch,located somewhere on the vehicle,off this switch one wire connects to your power side of the door solenoid direct,the other side of the switch goes up to your battery for power,incase you are locked out....Now if the battery dies,you hook a small jumper wire up to the back of this button switch and run 12v from and outside source direct through this switch to the solenoid and your in.
The last way is a emergency pull wire hooked up to the latch,run through the door and out either under the truck towards the hood or out the back towards the bed area....pull wire claw unhooks from latch and your in.
There is 3 ways i just showed to skin this cat..lol