Iphone 5 battery does not shows correct percentage

My iPhone 5 battery isn't showing the correct percentage as it should be. The battery percentage stucks at a particular level but the actual battery percentage is different. If I want to know the real battery percentage I need to turn off and turn on my iPhone to know the actual battery percentage.

For eg - Current battery 5%. I charged it for around 1 hour but it still shows 5% however the battery is actually charged around 70%-80%

For eg - Current battery 90%. I used it for aroud 2 hrs but the battery still shows 90% however the actual battery is around 5%-10%