Can an unplugged charger deplete the rechargeable batteries its used for?

sometimes when i have fechargeable batteries charging and they finish i leave them in the charger as extras and unplug the charger, when i do this i later on need those batteries i left in the unplugged charger, but when i use them they are completely dead. is it because i left them in the unplugged charger or do rechargeable batteries just do that?