Battery statistics reset on itsown..?

Anyone know why my statistics reset on its own..? Its not the first time it happand. Is it because i charged my phone from 62% back to 100%..? I red on apples official forum that apperently it resets battery statistics but im not sure, because i think some times i charge it from 80% and nothing happends.. Meaby i dont charge it to 100% but to 98% or something like that, so thats why it doesnt activate reset function..?