Daughter keeps complaining about her battery, even though it's a 7 and been used and plugged in whenever near a charger! It's about 18 months but is on iPhone upgrade program so covered by AppleCare+ Now new iOS has a battery %, I've checked and it's 84%. Is this ok or could I get a replacement with the cover? Or at least with the reduced price one at £25? Just wondering if this is at a decent level or one that Apple would replace for us.