Can I trade in my iPhone 7for a new iPhone

Maniakdex ~ See:

Sell, give away, or trade in your iPhone - Apple Support

Apple Trade In - Apple

But is your iPhone 7 really broken? – Perhaps its battery is simply depleted...

Does your iPhone 7 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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not sure how much they will give you for a broken phone try their trade in page

Apple Trade In - Apple