Can Li-ion battery outputting 3.7 volts each, damage my Xbox controller?

18650 batteries will not fit in the controller, since they are much bigger than AA.

I would suggest getting some rechargeable AA batteries (Eneloop or similar) and a charger (if you don't already have one.) Alternatively there are rechargeable battery packs specifically for the controller, which you can charge with a cable or an external charging stand, depending on the type.

The advantage of regular AA rechargeables is that you can also use them in other equipment, if required.

i would not use those 18650 batteries in a controller, its 3.7 volts but they kick out alot of amps too. i use 18650 batteries in my ecig which can sustain high output. they are also dangerous when used for the wrong purpose (18650 batteries are used in testa battery packs too lol). they would also most likely not fit as they are physically bigger than normal aa batteries.

I see, but most of the times i had 1.2V output batteries, so in total 2.4V. I didn't encounter any problems.
It's really common that normal batteries are have 1.2V output. EVEN MS in its controller package provides 2 x 1.2V batteries!!
Don't you find that strange?

under volting can cause stability issues in the way the controller works and may not have enough power for everything, it may even cut out when vibration motors start up.

Thanks for the reply,

i see. So im getting the normal ones i had already. Some Ni-MH ones.
Furthermore. do use see a problem when a single battery outputs 1.2V, so both 2.4V when Xbox controller needs 3V?