Learn Turkish: Kumandanın pillerini yılda bir mi değiştirirsin? - Do you change the remote control's batteries once a year?

It literally means "one in a year". In Turkish, regular frequencies are formed by taking a time period, adding the locative case suffix (-da/-de meaning "in/at/on"), and following it with a number. So, yıl (year) + -da + bir (one) = once a year. You can use this for other periods too, like haftada bir (once a week).

Why is the question particle mi placed after yılda bir instead of at the end of the sentence?

In Turkish, the question particle mı/mi/mu/mü usually goes immediately after the specific piece of information you are questioning. By placing it after yılda bir, the speaker is specifically asking about the frequency: "Is it once a year that you change them?" If they just wanted to know if you change them at all, they would put it at the end: ...değiştirir misin?

Why use the verb değiştirmek instead of the simpler değişmek for "to change"?

Değişmek is an intransitive verb meaning to undergo change itself (e.g., "The weather changes"). Because you are actively changing or replacing an object (the batteries), you must use the causative/transitive form değiştirmek, which means to make something change or to replace.

What is the breakdown of the suffixes in pillerini?