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Is there any problem if I let my iphone 4 battery drops to 0%? I remember for older smartphones, once your battery flattens out all your data is lost, because they are stored in memory.

While I understand that iphone shouldn't have this problem, but I wonder whether is there any problem if the battery goes flat?

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Not really. You won't suffer any data loss because the iPhone keeps everything on non-volatile flash memory. A complete discharge isn't great for the battery, but as long as it's not a regular habit your phone will be OK.

  • Apple recommends a complete battery cycle, so why would it recommend something which isn't great for the battery? – Graviton Nov 9 '10 at 15:08
  • @NguSoonHui: where are you getting that info from? Standard practice with Lithium-based batteries is to occasionally (say once every month or two) do a full cycle to recalibrate the battery capacity, but otherwise avoid discharging often. Lithium batteries degraded faster when fully discharged often and when they're hot. Optimal conditions are 40% charge and (I think) around room temperature or a little below, but of course its infeasible to maintain either of these in a phone! – drfrogsplat Nov 10 '10 at 8:35
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It should not be problem, but avoid leaving the battery in an uncharged state as this can cause it damage. The phone turns off before the battery is completely discharged anyway to guard against this just don't leave it for days like that.

Apple recommend having a complete battery cycle (go from fully charged to depleted and back to charged again) once a month anyway.

  • this is confusing; on one hand you said that complete discharge can cause damage, on the other Apple recommends complete battery discharge. So, whether I should complete discharge my battery once in a while? – Graviton Nov 9 '10 at 15:04
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    I see Apple's recommendation on the notebook page (apple.com/batteries/notebooks.html), I don't necessarily think it means complete discharge/recharge, I think it simply means you shouldn't leave the battery sit in a fully charged or fully discharged state. It should be discharged and charged at least once a month. For longterm storage it should be kept at a 40-50% charge level. – ghoppe Nov 9 '10 at 15:26
  • Spot on. I have seen a recommendation and explanation of discharge damage elsewhere. When the device turns itself off it has detected a minimum safe charge. The only thing that you should do from this point is recharge. If you attempt to turn it on again you risk damage to the battery. The point in the comment by ghoppe about storage is good advice too. – Kevin Nov 9 '10 at 15:44

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