Answer: 3,000,000,000.

Question: How many single-use batteries (aka household batteries or dry cell batteries) are estimated to be sold annually in the United States?

That's a big number. It averages to roughly 10 batteries per man, woman and child in the U.S., according to Environment Health and Safety Online, an aggregator of environmental information. When depleted, most wind up in landfills. Interestingly, California requires any battery to be disposed as hazardous waste, even though mercury has not been used in single-use batteries since 1996. In most states, single-use are accepted in household trash, though many communities provide occasional special-disposal events for these cells.

One option to consider: rechargeable batteries. No battery is perfect, but rechargeables edge us a little closer toward finding a portable power source that fulfills the 4 big wishes we would like to find in an ideal battery:

• Long life
• High performance
• Fair cost
• Environmental friendliness

Learn more -- probably more than you could have imagined -- about all types of batteries, including rechargeable batteries, in the REI Expert Advice article How to Choose Batteries. When should you recharge a rechargeable battery? How often? How many times? Answers await in our article.

I like rechargeables, but I routinely carry single-use AA or AAA alkaline batteries as backups. Choose household batteries carefully for your outdoor gear. Some lithium varieties deliver too much juice to some outdoor devices (particularly headlamps), so you need to know what a manufacturer recommends for individual devices.

Headlamps, flashlights and batteries have a wildly enthusiastic fan base. If that includes you, I'd love to hear your feedback on battery and power strategies that have worked for you during your outdoor adventures.