Time Lapse Photography using Smartphone (Part 2 - Android phone battery life)

As I have noted in the previous article, the most critical part in using your Android smartphone is to make sure the phone has power to take the photos!! This is especially important if you are going to use your Android smartphone to take time-lapse photography over days, weeks, months or even longer.

Assuming you want to take time-lapse photgraphy over a week or longer, I bet you won't be willing to use your latest and greatest Android everyday smartphone for this task, right? The risk that your newly purchased expensive smartphone getting damaged or even stolen during the process will simply make it not worthwhile, agreed? Plus, how are you going to answer your mobile calls while it is being used for time-lapse photography somewhere??

Even though it is rather stupid to steal a moden smartphone because one can easily remotely track its whereabouts using its build-in GP. For your information, there had been many reported cases where thiefs get caught within minutes to hours of stealing such devices. You can easily find these news using search engines.

Given the rapid replacement cycle of the Android smartphones, with the latest Android phones being outdated in 3-6 months, I am sure many of you have a perfectly functional old Android phones you have just recently retired.. So, it will cost you almost nothing if you simply install one of those free time-lapse photography on your retired Android phone, put it somewhere and start snapping time-lapse photos for fun. Since it is an outdated phone, the risk that it is stolen is low and I bet you won't panic or really care that much if someone actually come and steal it while it is doing its job... Plus you can still protect it by tracking it with free GPS tracking application, such as Lookout mobile security or similar, to make sure you can get even with whoever who steal it by reporting its location with the police.. Furthermore, it won't break your heart or the bank if the out-dated phone is damaged in the process either. As a bonus, since you are taking photos, even a phone with 2MP or 3MP camera would be sufficient to allow you to capture images with sufficiently high resolution to create high definition, e.g. 720p and 1080p time-lapse videos. If you really won't have an old Android phone around, it won't cost you much to snap one up on ebay or similar. Either that or you can retire your current Android phone for time-lapse photography and get a new phone ;)

Below, you will find battery life results I have made by using the very first Android phone, HTC G1/Dream. If I can do this with the very first Android phone, there is no reason your phone, newer than HTC G1/Dream won't work, right?

Before I present the results, you need to know that my HTC G1 is running EzGingerbread, Android 2.3.7 whereas the Nexus One is running Official ROM, Android 2.3.6. If your phone is run older Android OS such as Android 1.5, some of the time-lapse photography applications won't work because they require Android 2.x or higher. In such case, you can either install a custom ROM to upgrade your Android OS or you can simply use DailyRoads Voyager application. DailyRoads Voyager will run on Android 1.5 and it is free without any advertisements, until the time-lapse video feature is added in, you will need to use your computer to stitch up the photos to create the time-lapse video though. The HTC G1 is using a 2GB microSD card whereas the Nexus One is using a 16GB class 2 microSD card.

In order to reduce the experimental error, in my test, I am using the same phone with the same battery in all the tests. All the test are also conducted at the same location, so the time/power required for GPS fixes should be similar. In other words, I fully charge my battery using the USB port before I start the photo capture and the end time is when my phone's phone battery is completely flat, i.e. the phone shut down by itself. During the test, I do ocassionally turn on the screen to check the application is still running correctly and in some tests, the application may have encountered camera error and would need to be "restarted". Hence, when reading the results, you need to look at both the time and total number og photos taken. To save time, I didn't repeat the same test unless the result is obviously wrong. Having said that, I am confident that the result is representative of the tests with some margin of error. (I would be happy to incorporate your test/results in the table below if you sent me the data.)

In the results below, two applications were used for the tests. Tina Time-lapse was used running in foreground whereas Dailyroads Voyager was used in background mode. When WIFI was on, it was configured to never switch off using WIFI -> Advanced settings. GSM radio on means that the GSM SIM card was installed but 3G was not connected. GSM radio was turned off by putting the phone into airplane mode. Those results with > sign means the was some interruption during the test and the number reported should be slightly higher than as recorded below.

Based on the results above, we can make several interesting and perhaps useful observations

1. As many probably already knows, GPS uses huge amount of power and it is best to disable it to reduce power consumption.
2. WIFI when it is left on does uses extra power but its impact on battery life is still reasonably acceptable.
3. Taking images of lower resolution does not show measurable impact on battery life.
4. Increasing the time interval between shots does not results in measurable impact on battery life either.
5. Using an Android smartphone with faster CPU does not result in lower power consumption. The HTC G1 has a battery rated at 1100mAh. When everything is turned on, HTC G1 has a run time of about 3.5 hrs. When GPS and/or WIFI is switched off, HTC G1 can last around 5hrs. This means HTC G1 has a current drain of about 220-315mA. The Nexus One has a battery rated at 1400mAh. When everything is turned on, Nexus One only last about 4hr. When GPS and/or WIFI is switched off, it can last close to 6hrs. This means the Nexus One has a current drain of 235-350mA. Since the Nexus One have a larger battery, it did last longer compared to HTC G1 under the same condition, but it is obvious that the Nexus One's power drain is not less than HTC G1's. This means that a faster CPU makes little difference to battery life, maybe because the image resolution have also increased. 
6. Using different time-lapse application does not result in measurable impact on battery life. The difference is obviously within the experimental margin of error.
7. Even though photo taking with autofocus takes a few seconds longer than using infinity focus, it does not show significant difference in power consumption.
8. A fully charged battery can only take around 300 photos continuously. At 25fps, this is equivalent to a video clip of only 12 seoncds.
9. Leaving the phone's GSM radio on and connected to the network uses negligible amount of power.

Conclusions

As I have suspected, the major problem in using a Android smartphone to take time-lapse photo is the power requirements. A phone with fully charged battery can only last less than a full day of photo taking for a clip that last around 10 seconds.

To conserve power to take the maximum number of photos, it is essential to reduce power use. Based on the results, the first item you should turn off is the GPS because it can means the difference of about one hour battery life. If you don't have a SIM card installedin the phone, i.e. no 3G connection, it is best to turn on airplane mode to make sure the 3G/GSM are off to save power. If you need the phone to be constantly connected to the internet for monitoring purposes or remote tracking but can't afford to use 3G and your phone is within range of your WIFI network, it is best that you first enable airplane mode to switch off the 3G/GSM radio and then turn on WIFI but you also need to make sure you change the WIFI advanced setting to never turn off. If you turn on WIFI first then turn on airplane mode, you will notice that as soon as airplane mode is enabled, it will turn off your WIFI too.

If you must leave the phone connected to the internet for remote monitoring or tracking purposes, I would suggest that you should use 3G instead of WIFI because it seems that the 3G/GSM radio uses less power on standby compared to WIFI.

Otherwise, I would advise that you turn on airplane mode, so that it will shut off both your 3G/GSM as well as WIFI radio to save power. Also remember to turn off your screen too because it is another major source of power drain.

As the test result also shows, increasing the time interval between shots nor using different time lapse camera application nor reducing the captured image resolution makes no impact on battery life. This is probably because all the applications tested constantly utilises the camera and does not allow the phone to enter standby mode while the application is running. In other words, as long as your storage media allows, you can expect similar battery life whether you have your smartphone configured to take high/low resolution shots regardless how frequenctly they are taken.

Regardless what you do, you can expect that your Android phone's battery will barely make it through one day's worth of time-lapse photos, unless you have it plugged to a charger. Hence, if you are looking at making time-lapse photography over days and weeks, you are advised to setup a power point to charge your phone or use some very high capacity external battery to power your phone over the duration.

In the next article, I will explore the hardware tools and battery chargers that you will find useful if you are planning to take photos with your Android smartphone.

Suggestions for app improvements

1. Limited geotag would likely be sufficient for time-lapse photography since the camera, i.e. phone is not expected to move during the entire duration. E.g. simply recording the GPS coordinate in the first photo and uses the same coordinate in all subsequent photos/video would probably be sufficient.
2. Remote notification through e-mail, SMS, etc when the battery is low. So that one can plug the phone into a charger or external battery pack before the phone's battery is completely flat.
3. Reduce power consumption while taking time lapse photgraphy.