hmm looks like a Jolla

Yes, seems like some individual sold a Jolla battery in a Finnish online auction/second-hand store site, he stated there it came with his phone... Strange case, that.

EDIT: By the way, I searched for the extra battery TOH, and found out it already exists and works, but it is a DIY-project if you want one for yourself.

There are lots of battery manufacturers in China that would be happy to build the battery for you provided you buy enough pieces (and I think many could come down to some hundreds) and provide full mechanical information. The cell is a standard one, they just need to add the top and bottom plastic caps and the small PCB with the protection devices and the contacts. The price for such a battery is probably about $3 per piece.

Trumpeting "replaceable battery" without actually selling extra batteries, is... [erm... oops!]

When I broke the USB plug of the N900, I bought a second battery and an external charger. Wow, my life changed: I went out always with a fully charged battery. And a spare battery for those loong days out.

I did not (yet) vote anywhere for spare batteries, but I will be the first to buy one when Jolla store will sell it. I want the same "always going out fully charged" experience.

Maybe Jolla 2 will have replaceable battery, wireless charging, and no USB port.

Probably slightly more than that, but the Jolla battery is indeed a very cheap Chinese one ... I just can't fathom why they haven't ordered additional units.

Only reason I can think of is that they initially ordered a limited run of the battery unit, which was and is only enough to cover production of the actual phone and a very limited number of warranty battery replacements, and that no more have been made.

Again, Jolla's total lack of communication or indication of what's going on is very disconcerting.

mugen.co is producing good quality replacement batteries for mobile phones, they should be able to come with a replacement battery for Jolla. the only question is the quantity.

A Mugen battery would probably cost 2x as much as the dirt cheap one in the Jolla, if not considerably more than that. Unless Jolla paid them a considerable subsidy to produce one, the market would be too small for them to be interested anyway. Why they can't order a run of replacement batteries from their existing OEM is just ... weird.

Mugen is not expensive. I once bought a 1400 Mah replacement battery for mre previous smartphone (HP Pre 3) for a dirt cheap price at their web store. When I now boot up my Pre 3 (it's been a while, but sometimes just for fun and nostalgic) the battery is still at about 98% health. We're now at about 2,5 years since I bought that battery and close to 2 years of daily driver usage (the past months I've mostly been using my Jolla phone) so the quality is very good, esp. for that dirt cheap price.
(They also sold a well-priced 3000 MAh version but I didn't want to make the phone any bulkier lol.)

So no, it might not be more expensive for the Jolla phone (esp. because their sales of Jolla replacement batteries will be just as much as for the Pre 3).

FYI, I am now running my Jolla on a modified Galaxy S3 battery. The cell has exactly the same size and nominal capacity. From the comparison, and being an electronics engineer who has designed lithium-polymer power supplies and also a battery seller on eBay, I can say that the original Jolla battery sucks big time. If anybody is interested in knowing what should be done to adapt an S3 battery to the Jolla, let me know and I will describe the process (which requires a good deal of manual skill).

I'm not an expert with batteries, so I'm first of all interested in this statement. In what sense does Jolla battery 'suck' ?