I'd like to add something:
It's good to see there's been really good thought over the Jolla, good work!
The magnets is a good idea, I'm not too afraid of the influence on the electronics. Why: the magnetic field has probably been designed to be strong when close and decrease fast when far enough. When opening a HDD (I did, once), there's a strong magnet in it, approx 2 cm from the data disk. Does it erase data? No.
I work at ASML, on of our product contains a big plate (1x2m) with strong magnets inside. People with pacemakers/metals in thei body aren't allowed to come near (within 15cm). The magnet field within 15cm is strong, outside there's no(t) (enough) influence of the field.

What's bothering me is the possible influence of the magnet(s) on the battery: it could influence, but you won't see it and I don't want it to get on fire after a couple of months...

As I see on the movie, the movement of opening the halves isn't perfect/pure: it's not always going in a straight, controlled way to the other magnets. A groove/rib construction would make it better, maybe a magnetic bar between the magnets, so the halves are pulled softly against eachother.

Your problem with the magnets is, I think, it depends on the stable quality of the magnets and the influence of glueing/placeing on the endresult.

For example: you'll probably have variance in the flux your magnets can create. The fluxe you'll have in the end maybe depends on how much glue is used, the distance between magnet/plastic, maybe not position straight. It's completely theoretically, but it would be a pity if the design fails on this small issues.

By the way:
Congratulations, you're effort has been mentioned on Tweakers (dutch tech-site)