I don't think this is realistic. A half a ton battery in a sedan, shaped like a flat sheet, taking it out would require a quite elaborate system, which I am sure that exists in factories but gas stations are not going to invest in this. And different cars have different shapes and so will be the different batteries. If you lift half-ton batteries around there will no doubt be accidents. The infrastructure required to do this e.g. while six cars are filling up at a station all in five minutes? I don't think so. What about trucks? The batteries will be much larger. Small cars cannot have large batteries because the interior volume would shrink too much.
There was a company doing exactly that called Better Place:
https://en.wikipedia.org/wiki/Better_PlaceThey opened a couple of battery switching stations here in Denmark, but they went bankrupt in 2013. Tesla has also showed it and have a single station doing it, but I believe they've dropped going forward with the technology, they are betting on expanding the super charger network instead. I don't see why there should be a lot of accidents when the switch is done 100% automatically? It's basically like driving your car into a car wash.
Here's Teslas demo:
https://www.youtube.com/watch?v=FE81S26XG8cI understand that hydrogen is inefficient in that sense but in the future probably unlimited clean electricity will be available (nuclear fusion), so in the end it would not matter so much. EVs could be used for city traffic and people who need to travel long distances by car could use fuel cells (in their EVs) at a higher cost.
I do agree that fuel cells might be an advantage for long distance travel and trucks, and I can see why current oil companies would love for that to happen because that's quite similar to their current business model with tank stations. However, these hydrogen tank stations are quite expensive to build and hydrogen is quite difficult to store as well and if you think lithium isn't safe, what about crashing a car with a hydrogen tank at perhaps 700 bar?
As of now, because of severely limited charging infrastructure, and lack of incentives to build this infrastructure at every home, the use of EVs will continue to be exotic activity for decades to come, while the majority continue to burn diesel and gasoline and pollute like before.
I would bet building out a charging infrastructure is way easier, cheaper and faster to do than a similar hydrogen fuel cell infrastructure. Tesla is expanding their super charger network at a pretty decent pace and the other manufacturers have started building networks as well. Furthermore, there are various other companies that have been building infrastructure for years. The EU is moving too:
https://www.theguardian.com/sustainable-business/2016/oct/11/electric-car-charging-point-new-home-europe-renault"Every new or refurbished house in Europe will need to be equipped with an electric vehicle recharging point, under a draft EU directive expected to come into effect by 2019."
Batteries are getting cheaper and cheaper. Tesla and others are betting big on using them for home and utility scale energy storage and they can put up new systems at amazing speed:
https://electrek.co/2017/01/23/tesla-mira-loma-powerpack-station-southern-california-edison/ They installed it in 94 days:
https://youtu.be/hZzjuX6j2ME