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APPLE POSTS VARIOUS RECOMMENDATIONS on its iPad website to ensure a longer battery life for a hard-working iPad:
Don’t expose your iPad to extreme hot or cold temperatures—keep it between 32 and 95 degrees Fahrenheit. (In other words, don’t leave it in a hot, parked car, and don’t expect it to operate on Mt. Everest.)
Use your iPad regularly (not that you wouldn’t). And be sure to charge it at least once a month to keep that battery chemistry peppy.
Put the iPad to sleep to save power (press the Sleep/Wake button.)
Take the iPad out of any heat-trapping cases before you charge it up.
Manually close any apps you’re not using, as described in Use the Home Button to Switch Apps.