Best Answer: The best way to replace the battery on your iPhone 8 or iPhone 8 Plus is to take it to Apple. If you have AppleCare+ on your iPhone 8 or 8 Plus, then a battery replacement will be no charge. If you're out of warranty, a battery replacement goes for $49 normally for the iPhone 8 and 8 Plus. Another option, sometimes a bit cheaper, is to consider DIY, but this will void your warranty, so it's best for out-of-warranty devices. Or you can also find a local mobile phone repair shop that can replace batteries, but again, service from someone other than Apple themselves may void your warranty.Apple: AppleCare+ for iPhone 8 and iPhone 8 Plus ($129)