Common iPhone Issues：
While lots of things can go wrong with your iPhone, the two most common repairs are batteries and screens, according to iFixit.
"Based on Apple's projected life span, you can expect the battery in your iPhone to lose 20% of its charge capacity within two years," explains Kay-Kay Clapp,
iFixit's community and outreach manager. "Most of us upgrade our phones when our battery starts underperforming because we don't realize how easy replacing it can be."
And screens, which can easily break with a fall to the floor, are also simpler to replace than they seem.
"This used to be a tricky and time-consuming DIY — but starting with the iPhone 5,
Apple designed the display to come off first and that has dramatically simplified the repair," Clapp says.
The trick is you need the right tools (you'll notice your iPhone only has two visible screws,
and neither fit a standard screwdriver) and good instructions, since Apple provides none.
One thing you can't usually fix is serious water damage. While your old-model iPhone may survive a splash, dropping it in the pool is another thing entirely.
"Oftentimes water damage causes corrosion, which damages the components in your phone," Clapp notes.
Though conventional wisdom says a bag of rice saves waterlogged electronics by absorbing the liquid, it can't cure corrosion.
Cost To fix iPhone：
You know what a new iPhone costs: The latest model starts at $649 and goes up from there.
But many repairs, no matter where you get them done, cost less than that.
Let's do a rundown of the prices for the most common iPhone 6s fixes; we expect the repair costs for the iPhone 7 to match.
(Note that older models usually cost less, and larger screens typically cost more.)
For broken screens:
With Apple's extended warranty program, AppleCare+ ($129), you'll pay $29 to replace the screen.
Apple will replace your iPhone screen without a warranty for $129.
Replace the screen yourself with an all-new screen for $149.95 (which includes tools).
Prices at local repair shops can vary widely. Expect to pay anywhere from $100 to $250 to replace a screen.
For faulty batteries:
If your phone is still under warranty or AppleCare+, and the battery is at less than 80% of its original capacity,
Apple will replace the battery for free.
Replace the battery yourself for $44.95 (with tools).
Local repair shops, again, can vary, but expect to spend around $70.
Apple will replace your iPhone battery for $79 if you don't have a warranty.
In short, unless you're having very serious issues, the cheapest route is almost never going to be replacing your phone; repairing it is likely to cost less.
Even if you're uncertain of your DIY skills, even paying Apple for common repairs without a warranty is still more economical than buying a new phone outright.
If you're using a malfunctioning phone as an excuse to buy the latest model,
then by all means, don't let us stop you — but if you're looking to save cash, investigate repairing it rather than replacing it