iOS 4, Multitasking, and Battery Life

I recently got a brand new 4G iPod Touch for my initial foray into the amazing world of iOS. I’ve been sitting on the sidelines far too long and I’m so excited to finally have an almost-iPhone.

However, I ran into my first hitch this morning and my Google skills have proven useless to solve it. I’ve been using the iPod as an alarm clock for the past few days since its UI is superior to the ancient digital clock in our bedroom :). When I went to bed last night the battery was probably at 80% capacity. Apple touts that the new iPod has 40 hours of battery life when playing music—quite impressive. I had put the iPod in airplane mode, turning off the WiFi so that I wouldn’t get any mail or Facebook notifications. With no internet, no music, and no apps (supposedly) running, the iPod’s battery theoretically should have lasted for months—or even years :)

However, I didn’t wake up to the iPod’s alarm this morning. I woke up to Rachel pulling on my arm and saying “Wake up, Dad! I want cereal!” 1.5 hours later than when I was planning to wake up.

The iPod’s battery had died in less than 7 hours.

I’m assuming this is linked to the new multitasking system in iOS 4, where apps that aren’t running are put into memory so you can open them where you left off. Sure enough, I had like 25 apps in the multitasking tray, which I quickly cleared out after plugging in the depleted iPod.

So, iOS users out there: what experience have you had with multitasking and battery life? Is there an easy way to “officially” quit an application rather than send it to the tray? What should I do avoid something like this again?