I have a Samsung Galaxy Note 10.0. How long should it remain charged if I am not using it?

[AC Question]

I plugged the tablet into the charger, waited until it was fully charged, then unplugged it. I left it turned off, but the next time I turned it on, it only had 50% power. Is this normal? I have only had the tablet for a year and a half. After less than a year, suddenly it would not charge. I sent it to Samsung under warranty; they replaced the battery and the charger. It happened again about six months later; I sent it to the insurance company because the warranty had expired. They replaced the battery and the charger. And now when fully charged, it does not hold a charge. If anyone has any suggestions, I would welcome them. Thank you.