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I have an HTC Hero, which is a great phone, but the battery life is pretty poor if I'm using the GPS and music player on it as well. The phone uses a mini-USB connection for charging, and I have a Powermonkey portable charger just in case my phone runs out of juice.

But for longer rides, the extra charge and a half I get from the Powermonkey might not be enough - what other good options do I have? Either to charge the phone, or the Powermonkey, when cycling.

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Joke answer, but I can't resist. "How can I charge my phone while cycling?" Leave it on your desk, plugged into the wall. :) – Stephen Touset May 12 '11 at 20:12
As Wilka is from England, I'd imagine a solar charger wouldn't normally charge as fast as normal cell standby used it up. – James Bradbury Mar 12 '13 at 15:07
Using a phone as a GPS really eats up the battery life (especially if you leave the screen on for a long time), depending on what you use the GPS for maybe it'd be better to get a dedicated cycling GPS ($120 - $500, depending on features), which will let you conserve the phone batteries -- using my phone as an MP3 player with the screen off makes little difference in battery life. – Johnny May 17 '13 at 19:34
@DanielRHicks From what I've heard from the touring community, James Bradbury is right. Those solar chargers only work well if you're in a very sunny climate. Even partly cloudy conditions will reduce the charging to far less than what's needed to keep up with GPS use. – Carey Gregory Oct 31 at 0:26
@DanielRHicks Oh, I understand and agree, but solar chargers are mostly a waste of money for high-use devices like smartphones. They're great for other, less power-hungry devices though. – Carey Gregory Oct 31 at 0:54

10 Answers 10

Three options that I know of:

  1. AA cell phone charger (which you're already using) -- uses 2 or 4 AA's to recharge your gadgets. I use an Energizer model to charge my GPS for rides over 12 hours. Of course you need to carry enough batteries for the length of your ride.
  2. Solar charger -- can be mounted on a handlebar bag, a rear rack or hanging from your pack and typically has mini-USB connections for cell phones etc. No batteries required but won't help much on a rainy day. I've seen a variety of these at local outdoors shops.
  3. Dynamo hub charger -- this is probably the most expensive option, especially if you don't already have a dynamo hub. I'd like one of these (already have the hub) but the AA charger has been fine so far.
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It may be possible depending on your ingenuity to modify a Minty Boost (see my post) to accommodate all three of these methods of charging. A trawl around the internet might (or a visit to the forums on ladyada: ) might turn up something. – Amos Sep 3 '10 at 11:02
A good dynamo add on is the plug II by supernova. It gives you a usb port on your stem.… – Benzo Feb 26 '13 at 15:22
I have a portable cell phone charger that uses 18650 lithium batteries. It works great as a backup battery for my phone. These batteries are much better suited for charging cell phones than AA batteries. – Kibbee Feb 26 '13 at 16:53
Note for #1: When touring, you'd need to carry at most a backup set of batteries (2 or 4), AAs are ubiquitous can be found in the smallest of villages – Cog Oct 31 at 21:08

I have a HTC Hero which I charge using one of Ladyada's Minty Boosts (v2), when it gets caught short. This uses 2 AA batteries (which could very well be pre-charged rechargeables) to charge the phone (2 AAs give me between 20% and 30% of a full charge in about 30 minutes). I don't tend to charge using it while I'm riding, as it gets rather hot, and I'm not convinced my soldering is up to the job.

On the internet there are various instructions to modify Minty Boosts to run off solar power but on Instructables there's also a modification to run this off a bike dynamo.

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-1 for disposable batteries. Costly and environmentally ugly. – Carey Gregory May 19 '13 at 16:37

There is this company that sells bike powered phone charger kits. The price is very reasonable. I think this one may be suitable for your HTC because my husband has an HTC Incredible. Not sure if they would ship to UK.

I got the kit for his b-day because he also complained about the battery life. He uses stats app when he rides, and the battery would be dead in 45 min. I looked at reecharge as well but it was too expensive and kind of complicated.

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Probably the easiest way to fix your problem is to reduce the amount of power the GPS on your phone is using. By default, most GPS tracking programs eat up an enormous amount of battery because they default to maximum-accuracy settings. However, if you're going on long enough bike rides that you are worrying about battery life, you can probably afford to turn down these settings.

The way to do this is different with each of the different tracking apps, so I can't tell you exactly how to fix this, but if you dig around in the settings for a while you should find something. I know that the two apps I've used (Runtastic and My Tracks) have both allowed me to do this.

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I've found that doing that results in very poor accuracy. At least with the app I use (CardioTrainer) distance traveled can be off by 5%, which is really quite a bit (1 mile/km in 20). – Carey Gregory May 18 '13 at 15:52
In my experience, reducing the GPS sample rate doesn't affect the overall distance very much. What it does is makes it so that your path might show up say 20 yards to the left of where you actually went, but still parallel. Most programs have averaging of data points and trajectories of some kind, and should still work just fine with sampling rate turned down. – Gwenn May 19 '13 at 1:38
Errors in location from a low sampling rate are going to be random and equal in all directions, so errors in left-vs-right will also be seen in forward-vs-backward, and those errors will affect the calculated distance. And at least with the app I use, they definitely are. Like I said, I consistently observed about a 5% error on distances using the low sampling rate. – Carey Gregory May 19 '13 at 16:39

You might look at just upgrading your current approach—a lithium battery based cell phone charger (like the popular New Trent ones) generally go a lot further than AA based ones.

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+1 for a rechargeable solution. Using disposable batteries is a hideous solution, both in terms of financial cost and environmental cost. – Carey Gregory May 19 '13 at 16:35
Agreed, I use a Unu on my longer rides. Easy to strap to a tube or stash in a bag and run a cable. My phone right now is quirky recharging, so I use when stopped for a break. They charge phones pretty quick. – BPugh Aug 14 '14 at 3:21

check out

or you can go crazy and get a dynamo front hub and a charger from busch and Muller (Germany). this will cost you a pretty penny.

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There's a project on Kick Starter that looks like exactly what you're looking for: The Siva Cycle Atom

The funding ends May 23rd 2013, and they should start shipping towards the end of 2013. So if you miss the window to be a Kick Starter backer, you should be able to pick one up directly form them around then.

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I use a small external rechargeable USB backup battery. When the runtastic app & GPS run the phone battery down after 3-4 hours I connect the external battery for a few hours and it keeps the app going plus recharges the phone battery. I keep both the phone and backup battery in a small pouch on the top tube so I can hear the app say "distance, 24 miles: speed, 15.4 miles per hour" in a nice British accent.

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Check out this tech of my company Roadie Solar

They are new but very light and fits on a bike rack.

Possibly the lightest solar charger you can find on the market

We are doing a kickstarter Next week.

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Gidday and welcome to SE Bicycles. Interesting product, the price is incredibly unbelieveably low.. Do you own one? If yes, how do you find it? Do you have any association with the product? If so please note that in your answer. – Criggie Oct 29 at 21:32
@Criggie bump2pass is the originator of that product, as noted in their profile. – andy256 Oct 29 at 22:40
The community tends to vote down overt self-promotion and flag it as spam. If some (but not all) happen to be about your product or website, that’s okay. However, you must disclose your affiliation in your answers. Please edit your affiliation with this company into your answer. Otherwise, it is likely to be downvoted, flagged for moderator intervention, and possibly deleted. More about our self-promotion policies can be found here: – jimirings Oct 29 at 23:26

On my commuter bike, my front dynamo hub charges a small 18650 battery that I then can tap to provide power to my smart phone. You need to have an intermediary battery because most dynamos only produce the German government mandated 6VAC / 3 watts minimum, which is around 0.5 amps (500 milliamps) -- and this is only when you're going faster than 15 km/h. There are conversion losses going from 6VAC to 5VDC so you won't get the full 500 milliamps.

This is made worst because at speeds less than 15km/h, the voltage and available current drop to non-usable levels and the phone will stop charging and then start charging again -- on my phone the screen turns on and off each time there's a charge/non-charge event, which drains the battery tremendously.

In any case, most cell phones will want 5VDC @ 1A if not 2.1A, so the hub clearly can't produce enough power by itself for a steady charge. This is why you need the intermediary battery.

I designed and made the circuit** that I use for myself. You can buy something similar off the shelf here:

** I'd share the circuit except it's a bastard/hack and anyone who knows how to solder would be able to hack their own using a DC rectifier that takes the 0~6VAC and feeds 0~6 vdc into a LiPO charging circuit that charges the 18650; and subsequent boost regulator that takes the 18650's 3-4vdc to 5 vdc stabilized to a USB female A.

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92%+ efficiency is common for buck-down regulators, especially when input is close to output, so that max throughput 600mA will be close to a 550mA 5V regulated output that should suffice a recommended charge current for a ~1700mAh Li-* battery – Cog Oct 31 at 21:20
those 1A-2A phone chargers are/or should be smart-chargers and going over 1C (one full capacity) with a simple rectifier would permanently damage your device (at least it's battery) – Cog Oct 31 at 21:28
You can't just use a rectifier and buck-down because you only get 6VAC when going faster than 15 km/h. That may be fine if you are touring at a constant high speed but I use this on a commuter where I have to constantly slow down and stop. I found that I was actually draining the phone more because every time I stopped, the charge would stop and the phone would turn on and beep at me that the power cord was removed. This is when I redesigned the circuit so that there was a intermediary-battery to prevent the phone from cycling on and off at each stop. – RoboKaren Nov 1 at 4:22
Also, my phone will not charge if only given 500 mAh and running the GPS at the time. It needs at least 1A in order to not run down. – RoboKaren Nov 1 at 4:23

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