My wife and I just spent a few days doing a bit of late season sea kayaking. We were across Kachemak Bay from the town of Homer, Alaska. Due to the relative nearness of Homer, we knew we would have fair cell coverage from several places in and around where we were paddling. It seemed like a good chance to do some realistic field testing of the Biolite stove I recieved as a gift sometime back. What we found was that it would charge our phones, but it is a rather slow and tedious process.
As noted previously, the Biolite has an internal battery that runs a small fan to enhance the burning of small sticks. A thermal-electric device converts heat to electricity which keeps the stove's battery charged. Excess electricity is available to charge small electronic devices via a USB port. The problem is that the stove's internal electronics periodically diverts power to keep the stove battery charged. During this time, no power goes to the USB port. Thus your phone only charges part of the time the stove is burning. I didn't keep close track, but it seemed like the phone would only charge about half the time the stove was running.
My iPhone 4 was only partly discharged, and I could, over about an hour, top off the charge on my phone. My wife had let her iPhone 5 run way down. We were able to charge it up enough for her to retrieve some text messages. To fully recharge her phone would have been possible, but would have taken a loooong timmmme! Previous testing (at home) has shown that the Biolite does not put out enough power to recharge my iPad Mini, which requires more juice than a phone.
Key Takeaway Points:
1. The Biolite works fairly well as a small stove to boil water. Because of the fan, once you get it going you can even burn slightly damp wood.
2. It is too heavy for backpacking, but is OK if you don't need to carry it on your back.
3. It is reasonable to use the Biolite to top off a smart phone battery after modest use of the phone.
4. To fully recharge a very low phone batter would be possible, but would be tedious in the the extreme.
5. The Biolite would not recharge my iPad Mini at all. It just doesn't put out enough juice.
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"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz