I have been using Android phones for more than 2 years now. One of the biggest issue some people have with Android is battery life. Today I did some mini troubleshooting of battery usage on my phone, and thought I'd write about it.
I woke up in the middle of my sleep early this morning and I disconnected the phone from its charger because it had already charged to 100%. Went back to sleep and woke up after an hour or so. Guess what, the battery was at 92%! While the phone wasn't doing anything at all, it had lost 8% battery. That definitely doesn't sound good so I opened the battery usage monitor (Settings > About phone > Battery use) and found that "Android System" was the component that had been using most of the battery.
Android System is the component responsible for syncing email, calendar, photos, etc. I work at a company where I get 200+ emails a day on a normal day. I had enabled syncing of my work email two days back, and it looks like that's consuming a lot of power. Apparently my phone had been kept awake by Android System for 12 minutes and 38 seconds in the 1 hour period it had been on battery power (see screenshot). That's actually a lot. If I stop syncing my work email, my battery life would improve considerably.
Not all components we see in the Battery Use screen may be obvious, so let me try to explain some of them.
Display is obvious: power spent to keep the screen on. Android System does things like data syncing and VPN connectivity. Wi-Fi is the power used to be on wi-fi networks, including the energy spent to search for wi-fi network availability. If I know I am going to be in a place with no wi-fi networks around for an extended period of time, I turn off wi-fi on the phone.
Android OS is the energy taken by Android OS itself for its housekeeping. Phone idle is the power used by the phone to keep it running while it's sleeping. Usually Android OS and Phone idle are at the bottom of the list, i.e. they use very less power. If they show up in the top (and you have been using the phone for some time), something is probably wrong. On the other hand, if your phone has been sleeping most of the time, these components would be in the top because there wasn't anything else happening. When that happens you would have a lot of juice left in the battery too.
Cell standby is the time taken to keep your cellphone connectivity on. (This does not include the energy spent on voice calls because voice calls are tracked separately.) If I am traveling by road I'd be often going through places where there is no cellphone network. My phone would keep searching for network and connect to any available network only to get disconnected a few minutes later. When that happens, I have seen a good amount of energy being spent on Cell standby. In those cases I turn off data connectivity (Settings > Wireless & networks > Mobile networks > Data enabled), and that really helps.