iPhone always out of juice? Reset the battery indicator calibration with a full discharge/charge

There’s a lot of FUD around about iPhone battery life (and a lot of science involved in understanding the optimum recharge regime for Lithium-Ion batteries) but, even so, I was finding that my brand new iPhone 3G was getting down to around 30% after a just few hours of light use. It didn’t seem unreasonable if I was making calls but just sitting in my pocket?

In theory, the best advice on increasing battery lifespan comes from Apple and they do say that:

“For proper maintenance of a lithium-based battery, it’s important to keep the electrons in it moving occasionally. Be sure to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down).”

Then, one of my friends told me something that Apple doesn’t mention and it seems to have made a big difference to my indicated battery life.iPhone usage I don’t turn off Wi-Fi, 3G, location services, etc. unless I’m getting low on charge (because I actually want to use those features that I bought the phone for…) and I don’t have push e-mail since moving to GMail but, following my friend’s advice, I let the phone run completely out of juice and it took a long time to completely die after the warning messages for 20% and 10% battery power remaining. Then, after a full charge, my battery indicator seems to have calibrated itself to a much more realistic value (for reference, I’m on firmware v2.0.2).

Of course, usage patterns will vary but my iPhone is currently showing about 60% battery with 55 Minutes of use and 21 hours and 58 minutes on standby since the last full charge.

The iPhone 3G battery guide and charging tips post on Macrumors has a stack of information about iPhone battery life (including cited sources).

One thought on “iPhone always out of juice? Reset the battery indicator calibration with a full discharge/charge


  1. My iPhone 3G battery charge indicator has displayed that the phone is fully charged for the last 3 days. Then, it immediately displayed a warning indicating 10% battery life remaining. I couldn’t believe the battery was lasting that long, and obviously, it wasn’t. Does anybody know why this happened, and how to prevent it or fix it?

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