I have heard quite a few pilots opting for the paperless chart options
using the iPad or other e-book tools.  Below are some suggestions that
could keep the units up and running during a dark and stormy night
instrument approach:

10 Tips to Conserve iPad Battery Life
 
Apple claims a pretty impressive battery life for the iPad
<http://ipod.about.com/od/productreviews/fr/apple-ipad-review.htm>  - up
to 10 hours of use on a full charge. But that doesn't mean you won't
want to find ways to squeeze even more life out of it, or that you won't
have emergencies where you need to sacrifice some features to use the
device a little longer. For those situations, here are ten tips on
conversing iPad battery life.

1. Turn Off WiFi
Keeping your WiFi connection enabled drains battery, whether you're
connected to the Internet or not. So, if you're not connected - and
don't plan to be for a while - you can conserve the iPad's battery by
turning off WiFi. Do this by tapping Settings -> Network -> WiFi -> and
moving the slider to "off".

2. Turn Off 3G
Only some iPad models
<http://ipod.about.com/od/beforeyoubuy/a/ipad-model-price-comparison.htm
>  have a 3G
<http://ipod.about.com/od/iphonesoftwareterms/g/3g-definition.htm>  data
connection built in, but those that do run down their batteries when
using the always-on Internet connection 3G provides. If you don't need
to connect to the web, or need to conserve battery more than you need to
connect, turn off 3G. Do this by tapping the Settings app -> General ->
Network and then sliding 3G to "off".

3. Turn Off Bluetooth
You may be getting the idea by now that wireless networking of any kind
drains battery. It's true, so another way to save battery life is to
turn offBluetooth
<http://ipod.about.com/od/ipodiphonehardwareterms/g/bluetooth_def.htm> .
Bluetooth networking is used to connect devices like keyboards,
speakers, and headphones to the iPad. If you're not planning to connect
to any of those, turn Bluetooth off. Do so via Settings -> General ->
Bluetooth -> and moving the slider to "off".

4. Turn Off Data Push
This feature automatically pushes data like email from the web to your
iPad when it's connected to the Internet. Since wireless networking
always costs battery life, if you're not going to use this feature, turn
it off. You'll need to set your email to check periodically (if you want
to get email on your iPad, that is), but that's often a good trade for
improved battery life. Turn this feature off via Settings -> Mail,
Contacts, Calendars -> Fetch New Data -> and move the "Push" slider to
"off".

5. Fetch Email Less Often
If you're not using data push and want to get email, you'll need to tell
the iPad how often it should check your email accounts. The less
frequently you check, the battery it will be for your battery. Update
these settings at Settings -> Mail, Contacts, Calendars -> Fetch New
Data, and change the settings just below the Push menu.

6. Turn Off Location Services
Another form of wireless communication the iPad employs is location
services. This is what powers the GPS functionality of the device. If
you don't need to use that (don't need to get directions, use a
location-aware app like Foursquare
<http://ipod.about.com/od/ipodtouchapps/a/foursquare-app-definition.htm>
, etc.), turn off locations services via Settings -> Location Services
and move the slider to "off".

7. Use Auto-Brightness
The iPad's screen can automatically adjust to the ambient brightness of
the room its in. Using this feature will reduce drain on the iPad
battery because the screen will automatically dim itself in bright
locations. Turn this one via Settings -> Brightness -> and move the
Auto-Brightness slider to "on".

8. Reduce Screen Brightness
The screen brightness setting controls the default brightness of the
iPad's screen. As you might expect, the brighter your screen is, the
more juice is required from the iPad's battery, which reduces its life.
So, the dimmer you can keep your screen, the longer your iPad's battery
life. Tweak this settings by Settings -> Brightness and moving the
slider to a comfortable settings.

9. Turn Off Equalizer
The iPod app on the iPad has a music equalizer built in that
automatically adjust settings (bass, treble, etc.) to improve the sound
of music. Because this is an on-the-fly calculation, though, it drains
the iPad's battery. If you're not a high-end audiophile, you can likely
live without this being turned on most of the time. To keep it off, go
to Settings -> iPod -> EQ -> and set it to "off".

10. Auto-Lock Sooner
You can determine how quickly the iPad's screen should lock when it
hasn't been in use. The shorter the time before it locks, the less
battery you'll use. To change this setting, go to Settings -> General ->
Auto-Lock and choose your interval.