Right now, multitasking is not available on Windows Phone 7 as Microsoft believes that it would affect battery life. However, there are several ways which can be used to improve those runtimes. The best way to improve the runtimes is by turning off the features that come on by default. This includes edge and 3G radio, both of which chew battery juice rapidly.
Second is location service that keeps checking your current location automatically. You can turn it off by going into the ‘settings’ on your WP7 device. Also, if you know your current location, you can turn off the geo-tagging feature which is found under settings, applications, pictures and camera. Just tap on the button that says “include location information in picture you take”. As mentioned earlier, keep edge and 3G data off if you are not using them. In fact, in our testings, we found that using Wi-Fi puts less strain on the battery compared to the 3G. So, always prefer using Wi-Fi over 3G whenever and wherever you can.
We also suggest you turn off data roaming. This features comes pre-activated on your Windows Phone and can eat battery life as-well-as you wallet as it basically tells your smartphone to send data even when you are not in town. You can find it in settings, cellular and tap on data roaming options to select “don’t roam” from the list of options. Want detailed steps? Check out Kamal DS’ Windows Phone battery life article which contains step by step information on how to improve battery life of your lovely smartphone.