Thread: N9/x0: share how-to/workaround/mod/app/other
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0x4e84 is offline 0x4e84
2011-10-20 , 20:05
Posts: 55 | Thanked: 140 times | Joined on Mar 2011 @ Switzerland
#457
Originally Posted by moofang View Post
Hi guys, hope this hasn't been asked before (I've done some digging, didn't find it answered). I bought an N9 some days ago and the guy at the store told me that I shouldn't charge my N9 overnight. "2 hours maximum" or something like that so I don't "damage the battery". Very strange advice given that I've been happily charging all my phones overnight since the dumbphone era.

I've done some token research on the matter. I've noted that overcharging your Li battery _does_ in fact shorten its lifespan, but most phones including my trusty old N900 have something called "dual-mode" charging where it switches to "trickle charge" when the battery is nearly full, thus avoiding overcharging. Unfortunately I wasn't able to find convincing evidence that the N9 has this feature, although that could simply be because its a given for such a slick, modern smartphone.

The manual that comes with the N9 tells me that "You do not need to charge the battery for a specific length of time, and you can use the phone while it is charging". And yet, another section advices "Do not leave a fully charged battery connected to a charger, as overcharging may shorten the battery’s lifetime." (online version here)

I'm almost convinced that I can leave my N9 charging overnight, but I'll admit it - the small nagging doubt is losing me sleep. Can someone give me a definitive answer to this?
As a former hardware developer in electronics (in the mobile phone industry, incidentally), I can assure you that all "modern" phones manage the battery charging the right way and stop charging the battery when it is full.

Typically, the Power Management Unit (PMU) of a phone detects automatically which of the scheme should be used:
- Battery very low (voltage below a given threshold): Charging the battery at constant current, very slowly, because that's where you can damage it and reduce its capacity.
- Normal charge: constant current charging with higher current, and constant monitoring of the voltage (and generally the temperature, through a sensor that is built in the battery, hence the need of a 3rd electrical contact)
- Battery full, charger still connected: waiting until the battery charge has dropped below a certain amount before starting charging again (hysteresis principle, with 2 different thresholds for starting and stopping charging).

So, in short: no need to set up your alarm clock for unplugging your charger. Enjoy your full night of sleep without worries! ;-)
Last edited by 0x4e84; 2011-10-20 at 20:35. Reason: typo + further detail
 

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