Changing a key fob battery

[Orta]

Ok, so after ten years of 306 ownership this is the first time I've ever had to change a key fob battery. I removed old batteries a few days ago whilst I waited for my amazon bought energiser ones to come. They're the exact same as the ones I removed but I can't for the life of me remember what way they go in. I've tried seemingly every combination and nothing. I can't believe believe the fob has died as it was obviously battery related as it began winding down  they didn't  suddenly stop working. Anyone help? (Ps managed to lose the tiny screw when taking it apart!)