iPhone 3GS - NIMH 2X AA charging test

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Lucidus
 
Posts: 6
Joined: Sat Mar 23, 2013 8:12 pm

iPhone 3GS - NIMH 2X AA charging test

Post by Lucidus »

Duracell 2450 mAh NIMH AA batteries, removed from package and charged once.
iPhone 3GS completely discharged.

MintyBoost charged the iPhone normally for 1 hour and 15 minutes before charging stopped (battery voltage had dropped to 1.55 Volt for the pair just before charging stopped).
Phone now showed just below 50% on the green battery indicator.
Phone was then charged the rest of the way on a laptop, which should provide the same charging current as the MintyBoost (500mA). After an additional 1 hour 15 minutes the indicator had reached about the 90% point and then after about another 30 minutes the green battery indicator was completely filled.

As NIMH batteries do not reach full storage capacity until after 3 or 4 discharge/charge cycles, somewhat longer charging time may be obtained as the batteries are conditioned.

It appears that two pairs of this type of NIMH rechargeable battery should provide close to a full charge of an iPhone 3GS. (Note from my earlier posts that 2 or even 3 ordinary alkaline AA's will not charge this phone. As the support pages indicate, NIMH batteries can supply more current.)

I will post an update when available.

tempeleng
 
Posts: 2
Joined: Fri Apr 26, 2013 12:17 am

Re: iPhone 3GS - NIMH 2X AA charging test

Post by tempeleng »

Thank you for the write up. It's good to see some actual charging results. I have a couple of things I want to point out:

1) Is your iPhone 3GS battery new? Most cells see a 30% drop in capacity after 3 years.

2) The charge level indicators on most devices are mostly guesswork based on the measured battery voltage and the known mAh of a brand new battery. IIRC (can't find the original link) the voltage range allowed by Apple is 3.2 to 4.15. This is to ensure maximum usable battery life (in terms of charge cycles). When usage reaches 3.2v, the firmware will mark it as 0% and turn off the device even though in actuality the battery still has around 10-20% charge left. When charging reaches 4.15v the firmware will mark it as 100% and stop charging even though there's still another 5% left to charge.

tl:dr - You only need to supply 75-85% of the advertised battery capacity to fully charge an iDevice.
Disclaimer: Numbers are pulled from an article or forum/blog post I read a long while ago that I only found to be mildly interesting. I don't remember if it included devices sold by other manufacturers.

Lucidus
 
Posts: 6
Joined: Sat Mar 23, 2013 8:12 pm

Re: iPhone 3GS - NIMH 2X AA charging test

Post by Lucidus »

Tempeling - thanks for the reply and info.

My iPhone 3GS had just been returned to an Apple store for a battery replacement - they gave me a whole new phone, so a new battery.

I just did another MintyBoost test. 2450 mAh AA Duracell NIMH batteries. These were new and had been recharged twice, the last time about a week previously using a LaCrosse BC1000 charger at 200 mA. The iPhone had been discharged until it went dark. The first pair of AA's charged the phone to 61% (according to the iPhone indicator, which as you note is some kind of approximation). The iPhone was turned off, the cable disconnected, the next pair of AA's was put into the MintyBoost, the cable reconnected, and a strange thing happened. The iPhone turned on but did not start charging and neither was there a "This charging device is not supported" message. (Anyone else seen this happen?) I tried several times with the same result. Plugging in my 4 X D cell Alkaline battery pack led to normal charging, so it seems to be something to do with the AA's.

I then put the NIMH AA's through a discharge and recharge cycle on the BC1000 charger. When this was completed I put a pair into the MintyBoost and reconnected to the iPhone. This time charging started and continued from 55% indication to 100%. Whether the difference is b/c of the recharging of the AA's, or b/c the iPhone had been sitting for a couple days turned off I do not know.

So, it seems that two pair of 2450 mAh NIMH batteries will completely recharge a 3GS that has a new battery that was completely discharged, at least sometimes.

BTW, if I were to buy more NIMH AA batteries, I would only get the new type (Eneloop, etc) that hold their charge while sitting waiting to be used. But it would be nice to have a confirmation that this type actually does work in the MintyBoost to charge an iPhone. Can anyone report results?

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