Not quite too good to be true!
is this a legit battery? seems too good to be true..
Yeah, "extended batteries" are a thing, been around over a decade
In this case (and typically) it's 2 regular dimension/capacity cells in one wrap, each with their own protection circuits and with parallel wiring between those and the phone. Dead simple, they're all over the place, DIYable quite easily and safely if you have 2 new batteries:
Just parallel up the +/- terminals, keeping the wires as short as poss (ideally even length to the phone contacts, personally I'd make it flexible enough to flip them over periodically to extend lifespan).
Then play around with thermo contact until it's happy (obvs the hotter battery is the one closest to phone and it's contact will already be connected so no worries there)
Throw on a fatter cover or mod and done.
Only "too good to be true" bit is that in theory when one cell gets tired, it'll drag the other down with it, because the manufacturer won't have invested in a proper charge balance system (no need IMHO, would just shove the price up, cost space and probably wouldn't restore enough use cycles to be worthwhile if you were using sub-"premium" cells)
Speaking of price - as I've covered, this "tech" can be done for WAAAY under 24.00EUR. And I guarantee you Mugen etc aren't spending more than a couple of bucks per battery!
Generic extended battery covers are cheap, available and all made to fit a doubled up battery - Only exceptions are tripled-up batteries (much rarer than they used to be) and once I found a cool N4 setup with a standard size cell hiding under one twice it's surface area/capacity (same thickness) making for a unique-looking triple capacity battery with the thickness of two. Maybe they went to the effort of a charge balancer for that one, but even if they didn't, who cares! Legends.
Couldn't say which off top of my head but one of the contacts will be NFC of course, (so bear in mind if anyone goes there)
