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Anyone Know How to Wire 2 Batteries Together???

matthew2926

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I was reading on another site how some guy managed to wire together 2 iPhone 4/4S (not sure which) batteries together in order to give his phone double battery life. After reading up on circuits and similar things, I understand that the 2 batteries would have needed to be wired in parallel in order to increase the mAh while leaving the voltage the same. I was just wondering is anyone has tried this before or if anyone knows something about this. After opening up an iPhone 4 battery, I am pretty sure that all I would need to do is remove the connector on the second battery then use wires to connect the nodes from the battery without the connector to the battery with the connector. Basically, I would be soldering wires connecting the same nodes from another battery to the nodes that you can see in the picture. What do you guys think? Will this work? I'm pretty sure that it would but maybe I am missing something.

$photo.jpg
 

willerz2

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The circuitry in the iPhone were not made to withstand the amount of current from two batteries. Attempting to connect two batteries together will likely set your phone on fire. The failsafe in the iPhone may kick in, but you'd either have a really bad burn, or a whole on the side of your head where the phone exploded, no humor/sarcasm intended. Plus, if you link 2 batteries together, assuming it worked and is safe, your phone would be twice the thickness of the original design after you manage to secure the battery and make sure that the interior is isolated from the exterior as the rear-housing does when attached.
 
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matthew2926

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The several companies that offer cases with built in batteries for extending the battery life of your phone would be a better deal than trying to modify your phone.

I know but cases like Mophies only recharge your battery so much. In my experience, they are never as good as the internal battery. Adding a second internal battery would double your battery life.
 
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matthew2926

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The circuitry in the iPhone were not made to withstand the amount of current from two batteries. Attempting to connect two batteries together will likely set your phone on fire. The failsafe in the iPhone may kick in, but you'd either have a really bad burn, or a whole on the side of your head where the phone exploded, no humor/sarcasm intended. Plus, if you link 2 batteries together, assuming it worked and is safe, your phone would be twice the thickness of the original design after you manage to secure the battery and make sure that the interior is isolated from the exterior as the rear-housing does when attached.

But if I was to wire the batteries in parallel, the voltage would stay the same. The phone would still receive the same amount of power (no more, no less) but the battery would have a longer life. Correct? This is my understanding after reading up on parallel vs. series circuits. Also, I have a few ideas about how to solve the extra thickness but I'm not really concerned with this at the moment.
 

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I know but cases like Mophies only recharge your battery so much. In my experience, they are never as good as the internal battery. Adding a second internal battery would double your battery life.
My Mophie juice pack air charges the battery from 0-100%, giving twice the time between charges, exactly what you say you want with no more effort than sliding the Mophie onto the phone.
 

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But if I was to wire the batteries in parallel, the voltage would stay the same. The phone would still receive the same amount of power (no more, no less) but the battery would have a longer life. Correct? This is my understanding after reading up on parallel vs. series circuits. Also, I have a few ideas about how to solve the extra thickness but I'm not really concerned with this at the moment.

True, but the current required to charge twice as much battery would be double. It might be okay, but it's also possible that the adapter or charging circuitry in the phone wouldn't be able to handle it. If the charging circuit limited the current, which it might, then it would take twice as long to charge two batteries.
 
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matthew2926

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My Mophie juice pack air charges the battery from 0-100%, giving twice the time between charges, exactly what you say you want with no more effort than sliding the Mophie onto the phone.

Oh, sorry then. I haven't owned a Mophie in a while due to a bad experience with a Mophie for my old 4th gen iPod touch. They must have improved them. Anyhow, Mophies still cost upwards of $50 and I can get internal batteries on eBay for $6 so the cost makes it well worth it. Also, I have some experience soldering and I have already taken apart the one battery that I took the picture of. If all I have to do is solder some wires from one battery to another, I'm all for it. Plus, I really love fixing and working with devices, so I would personally rather save some money and give myself a project rather than just shell out some money for a similar product.
 
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matthew2926

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True, but the current required to charge twice as much battery would be double. It might be okay, but it's also possible that the adapter or charging circuitry in the phone wouldn't be able to handle it. If the charging circuit limited the current, which it might, then it would take twice as long to charge two batteries.

Wouldn't the charging current be the same since the voltage is the same? Since I charge overnight like most people, the extra charging time is really no skin off my nose. The way that I think of this whole project is taking a small gas tank and switching it with a larger gas tank. The only difference is that one can hold a lot more gas than the other. Because I would be wiring the batteries in parallel, the voltage would remain the same while the overall capacity would be dramatically increased thanks to the other battery. But I must point out that I am a high school sophomore with experience fixing iDevices. I was really wondering if someone with knowledge in the field of electrical circuitry and engineering could give me a straight "yes this will work" or "no this won't work." I know that this CAN be done because someone has already done it on another forum. My only problem is that I don't know exactly how he did it because he didn't post a tutorial and he hasn't been responding to recent posts. All in all, I have taken a look at the pictures that the guy on the other forum posted and have tried to figure out exactly what he did to create this double battery. After reading online about parallel circuits and studying images of simple parallel circuits on Google, the method that I posted in the original post is what I have come up with. I really want to know if it will work before I try it. That is the whole purpose of this thread.
 

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The battery looks like a particular amount of resistance to the charging circuit. If you've been reading up on parallel circuits you know that resistances in parallel always result in less total resistance than any of the individual resistances involved. And given the same charging voltage, Ohm's Law says that less resistance equals more current. I can't give you a simple yes or no answer as to whether this will work because I don't know the particulars about the charging circuitry in the phone, or how much current the adapter is capable of providing. The phone won't know that it's charging two batteries, but it will probably know how much current it's providing, and it may have a built-in safety that limits the amount of charging current. That's the variable that makes it impossible to answer your question. I've never used the units which have another battery built into the phone case, so I don't know if there's special circuitry that controls the charging so that only one battery is charged at a time. If they charge both batteries at once, then that answers your question. Nothing wrong with your project; I actually find it interesting.
 
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matthew2926

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The battery looks like a particular amount of resistance to the charging circuit. If you've been reading up on parallel circuits you know that resistances in parallel always result in less total resistance than any of the individual resistances involved. And given the same charging voltage, Ohm's Law says that less resistance equals more current. I can't give you a simple yes or no answer as to whether this will work because I don't know the particulars about the charging circuitry in the phone, or how much current the adapter is capable of providing. The phone won't know that it's charging two batteries, but it will probably know how much current it's providing, and it may have a built-in safety that limits the amount of charging current. That's the variable that makes it impossible to answer your question. I've never used the units which have another battery built into the phone case, so I don't know if there's special circuitry that controls the charging so that only one battery is charged at a time. If they charge both batteries at once, then that answers your question. Nothing wrong with your project; I actually find it interesting.

On the other forum, someone provided this link which shows a product that seems identical to what I am trying to make iXtreme T6 2840mAh Replacement Battery Does this prove that my idea will work? Also, the OP on the other forum had a working battery that he used, so this proves that the iPhone is capable of accommodating a double battery. By the way, I just realized now that I haven't give you a link to the thread on the other forum that I keep referring to. I would like to sincerely apologize for keeping you in the dark on this thread. Here is the link: [Moderator edit: Removed link to iPhone-related forum. Please read the rules. Thanks.]
 
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DaveM

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Okay, I read the thread through. It looks like OSU Engineering Student was already successful in the project. To reiterate, if the two batteries were in parallel you would not harm your phone. As you already stated, the voltage remains the same; you've just increased the mAH capacity. My educated guess would be that the charging circuit in the phone would limit the charging current, so likely no harm done to the phone regarding charging. It might provide more charging current than the one original battery would draw, but I doubt it would allow twice the current. That means that charging time would be longer than it would be for one battery, but that's to be expected. The discussion in the thread about charging in 10 minutes just seems, well, stupid to me. Sounds like a recipe for disaster. As for your question about soldering the corresponding battery terminals to each other, I can't respond to that because I don't know enough about the iPhone charging circuitry. Obviously, if there's 4 terminals on each battery then there's more here than just a positive and negative. Possibly two for current and two for sensing....???
I just don't have enough information to give you a definitive answer.
 
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matthew2926

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Okay, I read the thread through. It looks like OSU Engineering Student was already successful in the project. To reiterate, if the two batteries were in parallel you would not harm your phone. As you already stated, the voltage remains the same; you've just increased the mAH capacity. My educated guess would be that the charging circuit in the phone would limit the charging current, so likely no harm done to the phone regarding charging. It might provide more charging current than the one original battery would draw, but I doubt it would allow twice the current. That means that charging time would be longer than it would be for one battery, but that's to be expected. The discussion in the thread about charging in 10 minutes just seems, well, stupid to me. Sounds like a recipe for disaster. As for your question about soldering the corresponding battery terminals to each other, I can't respond to that because I don't know enough about the iPhone charging circuitry. Obviously, if there's 4 terminals on each battery then there's more here than just a positive and negative. Possibly two for current and two for sensing....???
I just don't have enough information to give you a definitive answer.

Alright, thanks anyway for all of your help. I really appreciate it. I agree with you, 10 minute charging is loads of stupid and never gonna happen safely. One thing that I thought of when coming up with my technique for soldering is that, if you look at any simple parallel circuit with a few batteries and a light, all of the - nodes are connected together and all of the + nodes are connected together. If you look at a simple series circuit with some batteries and a light, the batteries are connected so that the + nodes are connected to the - nodes. Because of this, I concluded that in order to wire the batteries together, I must connect all of the nodes from one battery to the corresponding nodes on the other battery. This way, all of the - nodes will be connected to each other, all the + nodes will be connected to each other, and all of the sensors will be connected to each other. I don't think that it really matters whether each node is +, -, or a sensor. As long as each node is connected to its corresponding node on the other battery, then it should be properly wired in parallel, right? Do you agree with my logic? By the way, I ordered 2 batteries for my 4S and some jumper wires off of eBay last night. I already have a soldering iron with a very fine tip so I will try making the battery as soon as the parts get here and post my results in this thread.
 
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