Willoughby's Established 1898 via Amazon offers Amazon Prime members the Sony Cycle Energy NiMH Rechargeable 1,000mAh AA Battery 2-Pack, model no. NHAAB2RN, for $1.80 with free shipping. (Non-members can spend $25 or more for free shipping; otherwise it adds $5.58.) That's 90 cents per battery and the lowest total price we could find for the pair by $6. These batteries come pre-charged purportedly retain 75% of their charge for up to a year.

Amazon Prime membership is $79 per year; however, Prime is free for college students for one year, and free for parents and caregivers for three months.