If there’s one complaint I hear about the daily use of the iPhone more than any other, it’s the length of time that the battery lasts. With the iPhone 4 those complaints subsided a bit but many people still remark to me that they have to charge it during the day or risk running low on power.

There are a lot of ways to help conserve battery life on iPhones and iPads but if there is one single tip that I can give to anyone complaining about battery life it’s this: Turn your brightness down to 49%.

This tip may not seem revolutionary to many of you that have owned iPhones for years but I can tell you that it has come as a surprise to many people that having the brightness set anywhere below the halfway mark greatly increases battery life.

My sister-in-law, for instance, was recently complaining that her iPhone 3G was simply dying on her about half-way though the day. Now, there are many factors that jumped to my mind. The iPhone 3G is older, so perhaps her battery was just tired, maybe she was multitasking 3D games heavily, etc.. But then I stopped and asked to see her phone.

R2XL.iPhone image 2011 05 25 12.49.53 520x780 The single easiest way to massively extend iPhone battery life

I unlocked it and was nearly blinded by the brightness of the screen. Her screen brightness setting was cranked all the way up to 100%! I slid it back down to the halfway mark and handed it back to her and she’s had greatly improved battery life ever since.

This tip works for the iPad and iPad 2 as well, although most iPad users are fine with the huge 10+ hour life of the iPad already.

You don’t even have to disable auto-brightness as it uses the maximum brightness that you have it set to as it’s ‘ceiling’, adjusting it up and down but not exceeding the maximum. Admittedly, the way it samples light for this setting is wonky, but that is a discussion for another time.

I will admit I haven’t done any scientific measurement to back this tip up, but I’ve been using this method to increase the battery life of my iPhone since the first-gen device and it’s proved to be a great help in allowing me to get through the day on one charge of the iPhone’s battery.

This tip definitely falls into the ‘So simple, why even mention it?’ category, yet I get asked about battery life constantly and very rarely do people know about this. The iPhone has incredible battery life compared to most of its competitors, yet it keeps coming up. Perhaps it’s because iPhone users tend to use their phones more aggressively, I’m not sure.

If you’re still using your iPhone on maximum brightness, give this tip a try and see how much it extends your battery life. If you already do this, sound off in the comments to let me know how it has worked for you.