Amazon offers Prime members the Sanyo eneloop AA High-Capacity Rechargeable Battery 4-Pack, model no. HR-3UWXA4A, for $13.39 with free shipping. (Non-members can spend $35 to qualify for free shipping; otherwise, shipping adds $5.74.) That's the lowest total price we could find by $9. These batteries can be charged up to 500 times and maintain 75% of charge after a year of non-use.

Also available for Prime members is the Sanyo eneloop AAA High-Capacity Rechargeable Battery 4-Pack, model no. HR-4UWXA4A, for $13.39 with free shipping. That's the lowest total price we could find by $3.