inside the key is a small 2mm by 3mm chip.If this has fallen out (which they do) it will stop the car starting.go back to where you changed the battery and find it otherwise you are going to have a large bill sorting it out!
Join the ford galaxy owners club for more info
www,fgoc,co,uk
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.