Pokemon GO guzzles your battery life like it's custard.
Go out with a full charge on your iPhone and you could run out of precious life juice before you've caught your first Caterpie.
Now, there are loads of things you can do on your phone to preserve battery but many won't apply to this game.
You can't use airplane mode or disable 3G or the game won't work. If you put on a short auto lock time or disable vibration, you won't be able to play properly.
But there are still loads of things you can do to make your phone last longer while you're out chasing down monsters. Here's what we've got.
Switch on low power mode
If you're running iOS 9, you can simply switch on a setting called Low Power Mode that instantly turns off loads of stuff to make your battery last longer.
Apple says "Low Power Mode reduces display brightness, optimises device performance, and minimises system animations. Apps including Mail will not download content in the background, and features like AirDrop, iCloud sync and Continuity will be disabled".
That should help a lot, but if you want to do more, or can't use Low Power Mode for whatever reason, do this...
Use battery saver mode
The game itself also has a low power mode. Tap the Pokeball, then tap settings, then check the "Battery Saver" option.
Now, this doesn't work automatically. You have to turn your iPhone upside down (the screen will go dark, and show the GO logo) to activate it. It will still track your location and vibrate when you get near a monster, but won't draw it on the screen until you turn your phone around.
Turn off AR mode
Also, flick the little AR mode toggle to turn that off. It uses your camera and various sensors to make Drowzee and pals appear in your bath tub. But if you turn that off you'll see the character on a generic background.
It's not quite as exciting, but it will save you a few percentage points.
Pokemon GO doesn't use Bluetooth so unless you've got wireless headphones or use an Apple Watch, turn that off.
Dim screen brightness
Screen brightness has a huge impact on your battery life, so turn that down. To quickly change brightness, flick open the Control Center by swiping up from the bottom of the screen.
Turn it down as far as it will go, as long as you can still see what's going on in the harsh glare of the sunlight.
Kill unused apps
When you switch to a new app, the old ones will hang out on in system memory. And while they shouldn't be using battery, that's not always the case.
If apps are playing music, using location services, recording audio, or checking for incoming VOIP calls, they'll run and sap your battery. Plus, Facebook is notorious for sapping your battery life.
If you want to avoid this entirely, just double tap the home button to open multitasking, then swipe the old apps up to fire them off the top of the screen until Pokemon GO is the only thing running.
Turn off background app refresh
Apps can do stuff in the background, like download podcasts and bring in new tweets. You can shut that noise right down with an option in the settings.
Turn off push emails
The one thing that won't change when you hit that toggle is email. To turn that off you'll need to go in the email settings and change it from Push (where the iPhone is always listening for new emails) to Fetch (where the iPhone will go out and look for emails at a specific time).
Disable app updating
This is another thing you want to shut down. Go into the settings, find the iTunes & App Store page, and switch off automatic downloads of updates.
Check battery usage
If you're still suffering, open the battery page in settings and fine battery usage. This will show you what's eating your battery. If one app is really eating away at your battery, stop using it, change the settings, or delete it.
Get a battery pack
And finally, go out and buy a battery pack. Either a case that you can slip your phone into, or a separate device.
Either way, nothing will save your battery like a dedicated box of juice you can use to recharge your phone midway through your journey.