Can I use an iPhone 6 battery

Better not. It's not safe. Besides, their size and the internal structure are not the same.

Sizes are nearly identical but the connectors are slightly different from what I see, you can try it for that extra 100 mAh but its better safe then sorry.

Hi, i already replaced my old iphone6 battery but still don’t get normal peak performance. It says your battery’s health is significantly degraded but my maximum capacity is 100%

hello, first ofall, it matters where the battery comes from, I bought mine on ebay from a seller claiming this was a used iphone battery pulled from an iphone. I’m not sure it’s true, but the battery gradually started working very well, it lasts 1,5days with bad network coverage. After installing new battery, for it to take the whole capacity, you need to discharge it to ZERO, and then recharge it for 12 hours. repeat the procedure 3-4 times. Second, it’s always good idea to hard-reset your phone from the scratch (don”t forget to back up). I set up mine as a new phone whenever I have glitches. Third, VERY CAREFULLY install apps while monitoring their behavior. there are battery managing apps in appstore that allow trickle charging of the battery. this helps putting more energy into the battery. lasts a bit longer too. Fourth, use ORIGINAL charger and reliable cable (I use amazon basics 6foot cable) the parametersof chargers differ from one to another. Then, never buy a woul-be extended capacity batteries with unbelievable figures like “3000MAbattery for iphone 6”. bigger capacity assumes bigger size. The only one thing will work if batteries are interchangeable like in my case : after a lot of research I installed iph7 battery on my iph6s, same desing, same connectors. but I don’t know a similar replacement for iph6. Hope some of these helps. good luck.

They don't interchange, Amazon has them.

please, who knows the exact dimensions of iPhone 6s battery? I know about different connectors, but what is its size? thanks

Go on ebay and they have one