While rechargeable batteries seem like a good idea, you're pretty much in the same boat as regular batteries if they die out on the fly...If you need to get powered up quickly and can't wait or don't have a way to recharge, you're going need to carry a set of replacement batteries with you anyway. I always carry a spare set of three lithium AAA's in case my SPOT II runs dry so I don't worry about guessing about battery life. Actually, It just happened last week while I was in the Smokies. The ON button started blinking red, I switched out the batteries, and I was good to go. Now, this is only the second time I've replaced the batteries in years but in the interest of full disclosure, I never use the tracking feature, instead just sending my "I'm OK" message from time to time so Mrs. Menhir doesn't worry and has a fair idea of where I am. I don't tax the batteries as much as other users might.