K10D Grip

Went out to the beach this morning with the dog and camera for a walk and took the camera along as well.
I was taking some photos when a helecopter flew overhead and so I thought I would grab a few shots of it but upon pressing the shutter button the camera refused to fire.
I looked to the lcd and found the battery had run out. The camera battery setting is set to grip first and I presumed it would then jump over to camera body but it just refused to do a thing until I set it to body first and then it worked.

Am I supposed to use auto?

I have it set to grip first so that I dont have to take the grip off to recharge the battery in the body.

When you have two batteries the K10D/K20D will pick one battery to use (depending on the setting in the menu). Once that one battery is dead the camera will show "flat battery".
You then know that battery has died and needs recharging

Turning off the camera and back on again should get the camera onto the good battery.

Don't forget too that battery life drops drastically when cold
EDIT: Oops - saw you are in Spain. I thought you might have been out walking here in the UK! Brrrrrrrr!
Matt

Tried that a few times and it just died on me each time.