By putting it in airplane mode! Don't laugh. Please read on.
The Sprint HTC EVO is the latest Android handset coming into the market. It is a first phone that supports 4G WiMax (though not yet available here in San Francisco). And it boasts a massive 4.3" display and 8MP video camera. But all the report coming in during its first week of debut confirm one thing, its battery life sucks. Some reports complaint the battery won't even last a full day of use.
The verdict aren't universal though. Some people got considerably more battery life than the others. How much people actually do with the phone is of course one major factor. But it also dawn on me that the battery life isn't determine by the phone alone, the network signal strength also play a large role. For those lucky folks who receives a strong signal, the phone exert relative little power to stay connected. Conversely when the network signal is weak, the phone has to increase the power of wireless signal to remain connected, thus draining the battery faster.
The signal in my bedroom has relatively weak signal. It bounces between 2-4 bars out of six. So I turn on the airplane mode when I go to sleep. Nobody want to receive a call while they are sleeping, don't they? I'm still using it as an alarm clock to wake me up in the morning, when I'd turn it back on to receive calls. In 3 nights it saved 24 hours of battery use for unneeded cell connection.
I wasn't testing how long the phone last while idling. I was using it every day. But I use it judiciously with the battery conservation in mind. Here are some of the things I have done:
WiFi off (except of short use)
GPS off (except of short use)
Phone calls a few minutes a day
Some web browsing
As a WiFi hotspot (several minutes a day)
A lot of music playing
Background syncing (e.g. Google Calendar)
10 minutes of GPS tracking
I think EVO's battery is adequate for me. It is worst than my iPhone, which routinely gets 3 days of life even after nearly two years of use. But EVO's battery is sufficient to me.
I want to mention that I've done all these battery conservation trick for my iPhone initially, including putting it into airplane mode during the night. Initially my iPhone 3G sometimes didn't last a day if I didn't use it carefully. After multiple OS update, its battery life has actually gotten considerably better. I hope EVO will also improve as newer version of Android comes out to make more efficient use of the battery.
(Update: the battery has lasted 3 days in my later test)