Originally Posted by
johnny99
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.
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.