As there is no multitasking, no app can run in the background to either drain battery, or monitor apps that may be draining battery. Native apps, like Alarm, can run in the background but they have all been optimized for minimal drain. Games really eat battery. You need to monitor what you do throughout the day and try to determine your total screen on time (vs sleep time). Depending on your device, that should be somewhere between 4.5 and 6 hours on a full charge.
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