How long should the battery of an iPhone 7 last? Approximately 10-12 hours depending on how you are using your phone. If you tend to use your phone more for audio playback and phone calls than internet browsing you can expect more out of the battery.
Keep in mind that the more recent iOS versions tend to use more power. When you purchase a refurbished iPhone the battery has likely been slightly depleted but at Frank We guarantee our batteries retain a minimum of 80% of their original capacity (which Apple has declared sufficient for efficient battery performance).
Apple's lithium-ion batteries are designed to hold at least 80% of their original capacity for a high number of charge cycles, this will vary depending on the product.