Quoted:
Looking for a 2nd battery for my D7500. I thought the batteries from my D7000 would work.......but they don't.
Where is a good place to get the correct battery, without spending $50???
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That's kind of the going rate for name brand OEM camera batteries across the board for current gen stuff. You can get offbrand ones, but they don't last as long or usually have the same mAh despite saying so. Mind you, the ones for my D850 grip, the D5, etc are $150 a pop, so it could be worse.
Depending on the camera, aftermarket batteries may or may not work anyhow. They are chipped on top of circuit protection, so it depends on a lot of things. Personally, I just run OEM. Makes life a lot easier in case of something happening and warranty/insurance is needed and I can say it is all OEM.