ASUS K55VD battery issue

Hello.
I wish to know this trouble: my ASUS K55VD when plugged in its power supply have the battery fully charged at 100%. At the next turning on the battery staus is at 99% also plugged into a battery charger. The next power on is 98% and so on up to 96%.
When it reaches 96% the led flashes green / amber and the battery status is always 96%.
I plugged of the power supply but the battery symbol is alway 96% until the notebook power off.
How does it depend?
I purchased two batteries but the behavior is also the same.
Please, can you help me?
Many thanks and best regards.