Replacing iPhone battery with NiMH cells: voltage and circuitry needed?

[Infinityze]

So for a DIY project I'm doing, I want to replace my iPhone battery (about 1810 mAh, 3.7V) with a NiMH battery (300 mAh, 1.2V) but I need help getting past some of the problems (and maybe more).
First of all. I've read that iPhone batteries are non-removable, is this true?
I've also read that I will require more circuitry to do this, but I'm not sure what.
Will the battery still run on 1.2V? If not, do I have to do something like put 3 of them in series?
Are there any other problems I need to work around?

 

[mfb]

Don't do it. You will just break the phone. Mechanically, but also in terms of its electronics.

- voltage has to be right, it won't work with 1.2 V. And your 1.2 V battery probably does not have exactly 1.2 V, so 3 batteries in series could give anything from ~4.5 V to ~3V.
- the battery has to be able to deliver enough peak current at a reasonable voltage. The built-in battery is designed for exactly this task, your other battery is not.
- the phone has a lot of electronics to monitor the battery to avoid damage to battery and phone. That electronics can give nonsense output if your battery is different in any aspect, with unclear consequences.

 

[meBigGuy]

Not sure why you want to do this. Could you explain?

mfb is correct.

1. NiMH batteries and Li-ion batteries have completely different charge profiles, so the iphone charger will not properly charge the batteries. probably damage the phone.
(by iphone charger, I mean the battery controller in the phone, not the wall wart or USB supply)
2. NiMH is 1.2V, li-ion is 3.6
2. You will never get decent power density with NiMH compared to Li-ion.
3. Fitting 3 NiMH batteries into the iphone will be impossible.
4. Depending on your iphone model, the battery replacement is non trivial even with a proper Li-ion replacement battery.