In new iOS4, we have fast app switching, and when we suspend the app, some data is still in memory and cost memory.
So, I just wonder if leaving data in memory will consume any battery life faster, comparing with using no memory? It will be good to know for programming the app to use less memory so that the whole iphone battery is better
I just want to know more about memory and battery than having any issue.
As far as I am aware RAM consumes the same amount of power no matter how much of it is used. It might be another matter if 1 "stick" (or whatever you want to call the hardware division in the iPhone) is entirely unused.
Theoretically, if your app has more data in memory, you might push another app's cached data out of memory, which could have some processing cost to restore if the user switches back. But I doubt it's measurable.
One good reason to reduce your memory usage when suspended is to reduce the chance that your app gets terminated to free up memory for the newly running app.
Another simple way is to test the iphone's battery usage by leaving it on with more memory content for longer time, new ios4 can display battery % that may help you notice the battery consumption over little longer period of time.