These are the ultimate re-chargeable AA batteries!  Unlike most rechargeable batteries, these are made from Li-polymer meaning they can be discharged fully and re-charged many more times, ensuring they last a long time.  They conveniently re-charge using the very common microUSB connector (4-way cable included!), so anywhere you have USB you have a charger.  These work great with our solar chargers if you need to keep them charged off the-grid.  These will work in anything requiring standard AA batteries.