Battery indicator on iphone shows 100% full until it dies.

Battery shows 100% full until phone dies then shows the battery is empty with just a thin red line as normal, when plugged in for recharge it shows 90% instantly and only takes 5 mins to show fully charged again. Obviously it isn't charged fully and if I leave it charging for an hour or so it will last for a 24 hour period. Have backed up on iTunes and done a restore, this has had no effect on battery indicator and it remains the same as I have explained.

Any help would be appreciated.

Julian.