Sleep mode is fine. It uses barely any resources... and hibernate mode even less. Basically, these modes leave your windows open and any work in progress stored in system memory, which then takes barely any power to maintain.
I usually leave my laptops plugged in when not in use, which isn't a great practice for optimum battery life. A practice to keep batteries lasting longer before they need replacement is to set the charge system to shut off at about 80%. I'd think most laptops have this feature. I don't know why I don't have it set. Lazy, probaby.
To corroborate my comment about sleep mode, I'll do a simple test. I will put a fully charged laptop in sleep mode then disconnect the charger. I'll then leave it be overnight or longer and see what the battery percentage of charge is. My guess---90-98%...
