Sorry I haven't replied earlier (been too busy stocking up on batteries for my 2 keyfobs haha . Since I posted in December, I've now had 7 batteries in both fobs, I have to carry spares in my phone case, every coat I own, my handbag and drawer in my office. I had another issue in March with the reverse camera failing so took it to my nearest Hyundai dealer and they replaced with a new one as the car was still in warranty (just), I mentioned at the time that I'd had only replaced the battery the day before, anyway, I had no problems until this weekend, I drove to a friends in the country and parked up, 2 hours later went back to the car and clicked 'open' on the fob and nothing happened...after nearly half an hour, my friend drove me to the shop and I bought a new battery (the one with the bunnies on the advert), but it still didn't work, then my friend happened to press the boot button at the same time as I clicked open on the fob and it opened, I went home and the next day went out again, got out of the car, locked it, came back and less than 24 hours after replacing the battery, I was locked out again. So far this has happened with both the main key and the spare, so I've just called local Hyundai dealer and they've said to take the car in and they'll put one of 'their' batteries in to see how long it lasts, they are also going to show me how to access the hidden lock (without scratching the bodywork).
Honestly I love my car on the whole, but after once occasion getting stuck with my 2 small grandkids with me I'm getting to the stage where I think I may as well just leave the car unlocked (joking....not joking)