When I’m done reviewing a phone, there’s usually not much to do with the thing but let it collect dust on a desk. But what if that idle time could yield extra insights?

That led me to the most boring research I’ve ever conducted: configuring a series of loaner smartphones in the same way (WiFi on but not connected, Bluetooth on but not paired with anything, set to check Gmail and Yahoo mail accounts), then seeing how much of their battery was left 24 hours later. Some Android phones required an add-on program, the free Gauge Battery Widget, but otherwise I left these devices as they arrived.

Here are the results:

AT&T iPhone 4: 95%

AT&T HTC Inspire: 88%

Sprint HTC Evo Shift (4G on): 66%

Sprint HTC Evo Shift (4G off): 77%

Sprint Samsung Epic (4G on): 74%

Sprint Samsung Epic (4G off): 73%

T-Mobile Nexus S: 47%

T-Mobile Samsung Galaxy S: 88%

Verizon iPhone 4: 93%

Verizon Motorola Droid 2: 80%

Verizon HTC ThunderBolt: 57%

Those numbers proved one thing early on: Google needs to work on the standby battery life of its Android operating system. The two iPhones I tested outperformed Android devices by a sizable margin. (That’s not necessarily a reason to buy an iPhone over an Android phone. It is a reason to keep your charger handy if you go with the non-Apple option.)

But the difference between the iPhone and the average Android was dwarfed by the variation among phones running Google’s software. The ThunderBolt may have a deserved reputation for poor battery life, but T-Mobile’s otherwise remarkable Nexus S did even worse in my one test here.

What about BlackBerry phones? That’s just bad timing. The two review BlackBerries I’ve had anytime recently went back to their respective PR departments months ago. But I welcome you to repeat this test yourself and share your results in the comments. I’d also like to see your own numbers for any of the Android phones I tried out.