What sorta batteries (from different phones) fit in 2016 iPhone SE.

@ummmiguessso, the short answer is none. The only battery you can use in a 1st generation iPhone SE is a battery made for a 1st generation iPhone SE. Every time a new phone comes out, the battery is custom designed to take up all available space inside, because the bigger the battery, the more mAh it can hold.

So right there is your reason it won't work; if it has more mAh, then it's bigger, and if it's bigger, it won't fit inside your phone; that's just physics.

That's beside the other considerations like the particular sensors built into the battery and the placement and type of connector to plug in; Apple uses a few different plugs and they're not all compatible. And the flex cable that leads to where it's plugged into the logic board is made to fit very carefully, so if they move that connector even 1/8" it will no longer plug in.

Anyway, there's a whole bunch of reasons why you can't use a different battery, so don't bother wasting your time looking for an alternative because there really aren't any. Over the years there have only been very minor advances in power density for Li-Ion batteries, so you may come across one that offers a small percentage increase in mAh, but if you run into the so-called "gold" batteries that claim something like double the power rating of the original, you can be assured these are scams. Like I said if you want a battery with twice the power you need a battery that's twice the size. One of our esteemed volunteers, @oldturkey03, has written a great article about those fake batteries.

The myth of the "high capacity" batteries - iFixit Repair Guide