New batteries.

Eneloops are what I've stocked up on. Low self discharge is great, not prone to leaking and corroding and ruining devices like alkalines do is great.
I think nowadays most rechargeables will come ready to use out of the package as the tech has improved for low self discharge. They are not charged to 100% iirc at the factory. Maybe shipping/warehouse/store shelf sitting stability is the reasoning.