Hello

I'm using my Samsung Galaxy Nexus (currently running Android 4.2.1) more and more as GPS/NavSat when going for a ride since its screen is much bigger than the Garmin eTrex 20.

Before selling the Garmin, I have a couple of questions:

1. Can an external battery be hooked to the Nexus USB port and provide power for a full day with GPS on and frequent screen use? Currently, I keep turning GPS + screen off as much as possible since the battery can't last for a day's ride, and changing batteries is a PITA.

What about the New Trent 12000mAh recently reviewed by the London Cyclist recently?

2. Is there a good utility that can record a trace, so that I can later see where I went, and see/share the results on Google Maps?

Thank you.

Yes, you can plug an external battery pack into a Samsung Galaxy Nexus using a standard microUSB charging cable. I don't see the point of leaving the screen on all the time, but if you really need to do that, your 12000mAh battery should be more than adequate. You can also find well reviewed 10000mAh batteries from various sources for around US$40 (search for the Anker 3E on Amazon). Look for battery pack that have ports designed for Android, which do seem to work better than ports designed primarily for iphone.

MyTracks is a popular Android app for recording your GPS route and later uploading it to Google Maps. There are others apps that upload your position in real time, though the battery cost is probably higher than with MyTracks.

Remember that any cell phone GPS is not going to be as accurate as a dedicated Garmin GPS unit, especially around tall trees or tall buildings, but the differences may not be important for recreational cyclists.

Thanks for the infos.

I don't leave the screen on all the time, but I noticed that Maps takes several seconds to show my precise location when switching the screen back on. I assume it's a trick to save battery, since users normally don't care about GPS once the screen is switched off and usually forget to switch GPS off.

From experience, that smartphone's GPS infos is accurate enough for my use. I only use it while riding around in the country.

What do you mean by "battery pack that have ports designed for Android, which do seem to work better than ports designed primarily for iphone."? That the pack was designed for Android or because they have microUSB instead of the proprietary Apple plug?

Google Maps only uses the GPS when your phone's screen is on, but track recording apps will use the GPS continuously, even when the screen is off.

The USB standard is for 0.5A of current, however, that is not enough to power a smartphone with the screen and GPS both on. Most Android phones can work with 1.0A or even higher, but only through special circuitry in the battery pack (which is different from Apple-specific circuitry). The battery pack's specifications should tell you if it can do this. Some battery packs have 2 output ports, one with high-current Apple-specific circuitry and the other for Android devices. If you plug your cable in to the wrong port, you only get the default 0.5A.

Thanks for the clarification.

I notice that the Anker Astro3E delivers 3A while the New Trent IMP120D delivers 1A.

Does it mean that an electric device doesn't care it it's fed more amps that it needs, or is there an upper limit to the Ah the battery should deliver so that it doesn't harm the device?

Not sure why OP would want the screen on all the time either, but I have the extended use battery installed in my Nexus and have no problems going over 12 hours with Stravia app and Navigator working. There are some battery tending apps that can help with the battery life but I have found the biggest factor is whether the phone struggles to receive 4G over 3G - the second factor is the screens brightness which can really suck the battery juice. And turn off Bluetooth and WiFi if you are not using it on the ride.

If you aren't using data, you can turn that off too. (If you are just tracking, you don't need maps.)

Thanks. I don't keep the screen on at all times, but I do have to turn it on more often than in the city.

What "extended use battery" do you use? A bigger internal battery than the default?

When riding around on day trips, I also make sure I turn off wifi and bluetooth, and use 2G instead of 3G since apparently, Android only needs a data connection to get a head start when enabling GPS but once it knows where we are, it only relies on GPS so I could even turn off the data connection as long as I keep GPS enabled?

Yes, and I replaced the first extended battery after one year, made a big boost in my uptime which was always good on the original extended battery, but I am not sure exactly why the 2nd new extended battery was 25% better from day one. Better battery construction in just a year? The new extended battery comes with a new slightly larger back cover for the Nexus.

Thanks. I think I'll go for an external battery because the original is good enough for daily use.

BTW, I notice that the Anker Astro3E delivers 3A while the New Trent IMP120D delivers 1A.

Does it mean that an electric device doesn't care it it's fed more amps that it needs, or is there an upper limit to the Ah the battery should deliver so that it doesn't harm the device?

Some devices need higher amperage to charge.

Devices draw what ever amperage they are designed to draw.

The power source needs to supply at least as much as the device can draw.

I think that is correct on all smart devices chargeable by USB, some Ieee standard - it "should be" correct, however I am reluctant to go on record saying it always does because this is exactly the kind of thing that can fry your electronics! Anyway OP, if you have the space needed to put a short USB cable to an external battery pack, and make it stay attached, (big hassle with my Nexus on my car charger), go for it!

I believe it's different voltage that causes this problem.

Yes, the voltage must be exactly (probably +/- 10%) what the device expects, but apparently, the battery can provide higher Ah and the device will simply consume whatever amps it needs to run.

Indeed, it's something I worry about, which is why I'll buy an angled cable if not provided by the big external battery.

I saw these on the D/X web site and thought they might work well with a smart phone to extend battery runtime. I didn't buy one but only because I have a Garmin now as well. The only thing I don't like about the Garmin is that the mount is not quick release. That's a pain because now I can't mount my smart phone unless I cut the plastic ties on the Garmin mount. Yeah, I can buy more ties but it is still a PITA to do that every time you want to change devices. The holder used for the smart phone just uses Velcro.

Thanks for the link. The Nexus uses a regular microUSB so the other options look good enough and provide more current. Judging from the original 1750mAh battery, 3000mAh might last about a day.

happened to have a scooter battery around so I built that. Car usb charger rated at 2 amps. phone will draw 2 amps charging as well. Found 1a at 5v won't charge and run the screen on at the same time.

Found this new dynamo made for cell phones,... https://www.kickstarter.com/projects/...fe-one-pedal-a

Good to know. Thanks for the info. That's why it's faster to recharge a phone using the transformer provided with the phone instead of just plugging the phone to a PC through USB (500mA).

Definitely phones charge faster on a plug in wall charger ( as well as most plug in car chargers ). I suppose it's better if the ( external ) battery has a larger maximum current output so the device can operate power sucking apps and charge the internal battery at the same time. Most Li-ion batteries are not recommended to charge at a rate over 1000ma. Not to worry though, I'm sure the devices are designed to limit current to the battery while charging regardless of how much current supplied by the external battery. Then again I'm no cell battery expert. Depends on the chemistry of the cells used as to what maximum current can be used to charge the internal battery. Li-Po can certainly use higher charging currents.

I've noticed that when I charge my phone from a wall ( or car ) power source the phone battery will charge faster, at least till it gets to the 80% mark. After that I can tell the device slows the charge the rest of the way till fully charged. Built in smart charger I suppose.

No, it doesn't work that way. Amps cannot be "fed". I.e. the battery cannot somehow forcefully shove any excessive amps into the electronic device. The current flowing from the battery is determined by the effective voltage of the battery and the impedance of the consumer (the good ole Ohm's law). The latter is what will change depending on the device's power demand (as the device demands more power - like when the screen turns on or when GPS receiver activates - its impedance drops, which causes more current to flow from the battery). The amps will always be exactly as high as necessary, i.e. as high as the electronic device wants them to be.

In simple words, it is the consumer that plays the active role in this case, while the battery plays passive role. It is the consumer that "requests" certain current, not the other way around. The battery will always "obey" that request precisely (as long as the request does not exceed the battery's capabilities). The current will be exactly as high as the consumer wants it to be. The battery cannot "feed" more current than the consumer requests. It is simply not possible.

True but things can happen. When I first bought my phone I ended up having a problem with the USB cable that was provided to charge my battery. Occasionally I would remove my phone from the USB charger and find the battery completely dead. Most of the time it worked fine but when this would happen the phone would feel real hot and I knew something had to be wrong with the cable ( or the phone battery ). I got rid of the cable and bought a plug in wall charger. Since then no problems. No doubt now that somehow the cable was shorting out the battery and completely draining it. Certainly some sort of thermal runaway was going on when this was happening. I can't think of any other reason why it would get so hot..( It was VERY HOT )

Thanks for the infos. I did understand that it is the device that determines how much current is flowing from the battery, but didn't use the right wording.

Anyhoo, a 12000mAh external battery should be enough to power my Nexus for at least a day of full-time GPS use.

Yes, I suppose it would but the question is, "Do you really need a battery THAT BIG"? I'm not the expert on power usage for cell phones but I would think something in the 3000 to 4000mAh range should get you through the day for most rides. The only other reason I can think that you might need something bigger would be for something like a century or 24hr event. For a 24hr event that dynamo with USB charging option would look real good.

Mmm, you're right. There's no need for that much power since I'll just plug the phone/battery at the hotel at night.

Anker also makes 5600mAh and 8400mAh external batteries.