Your thread title said "...for Touring?" You are not touring. You are commuting. Riding around town. Etc. There is a big difference between "Touring" and riding around town. Different bikes, different gear, maybe different clothes too. If someone asked which panniers to buy for riding around the world and which panniers to buy for going to the grocery store, I might give slightly different answers. And if someone asked which bike to buy for touring around the world and which bike to buy for commuting to an eating place in the evening, I'd likely give a different answer. My original comments about needing six different lights on a touring bike still apply. You don't need them. Touring is a daylight activity.
Please change the title of your thread to "3 AAA Battery Bike Lights Vs USB Battery Bike Light for COMMUTING?"
Touring, vs commuting could make a difference if the usb light has a short battery life.
However, the Petzel light I'm using last's a good long time on a single charge. If you're touring, it'll last waaaaay longer than it would commuting because you wouldn't be riding at night so often, though you might use it for other tasks such as setting up camp. I think it's about 6-8hrs of use per charge depending on how aggressively you use it. I use mine in auto-brightness mode, so it brightens and dims based on lighting conditions... Be aware that it will dim for on-coming headlights. Avoid this by looking slightly towards the road shoulder. However I usually I don't need it at full brightness for riding in the city. I mostly only keep it on to warn drivers entering from the side streets of my presence, since their headlights don't pick up my reflective gear until I'm almost in front of them (and even with me consciously shining the light at the driver, I've still had close calls). I don't need it to see the road with streetlights everywhere, or even in rural areas when the moon is bright, but I also have good night vision.
So this brings us to power supply while traveling.
For commuting, charge it while at work or at home between uses just like your other devices, and never worry.
When traveling longer distances, remember that many places now have free wifi... typically power outlets are found in abundance in these venues, sometimes even USB ports, like most of the new Dunkin Donuts and McDonalds. Order a coffee and choose a seat by an outlet. With careful usage you can keep it charged this way.
Because there are places you can't count on that though, and some long stretches of country where there's nothing and no one, another option is GoalZero... Their Venture30 USB battery is waterproof and will charge both my Petzel and my Bluetooth headset using less than a fifth of its capacity. For reference the Venture30 will charge my Samsung Galaxy 2s Tablet to about ¾, but my Galaxy 2 smartphone used to get 1⅔
The Venture30 itself takes about 6 hours to charge fully when plugged into an outlet however, and much longer using the solar panels, but, with the solar panels in full sun you can charge the light and the battery simultaneously while you ride. They do have larger solar panel options, and a package that includes the Venture30, or you can buy the Venture30 on its own.
I bought 2 sets of panels, since they can be linked together, and I clip them together and bungee them over my rack trunk, so I end up with one facing left and one facing right to increase the odds that one would be exposed to the sun as I ride, no matter which direction I'm riding. And yes they do add some weight, and no they aren't cheap.
For commuting, the panels are worthless, unless you consider the conversations they attract as having some value. In that case they do make good conversation starters, in addition to the usual, "how far you going?"
For the reasons above, they're best for long multi-day rides as long as you don't mind the weight. Every bit you charge as you go stretches your time between needing to plug into a wall.
Note too that Winter daylight hours in the northern latitudes are not long enough for effective solar charging, but in an emergency, it can provide enough charge to get a quick message out via SMS on a cellphone or tablet right away, or if you wait longer to charge more, you can use the GPS or internet for a while.
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