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Correct Battery Operating Voltage (Leak?)

I work for a major repair chain and the company practice is to replace batteries that test over the rating on the battery which is 3.8v calling it a voltage leak however I always believed that 3.8-4.2v was the operating voltage with 4.2v being 100% charged. Batteries are not designed to resist voltage to my knowledge, they are just an open gate unlike a step down transformer. I charged a battery to 100% in the phone and then tested the voltage which read 4.2v however I also have a Kaisi battery activation and charging board. That will charge a battery to 4.33v and then stop, so can anyone confirm this?


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Can you explain this policy a bit more…it seems rather uninformed.

A Li-ion battery has a nominal voltage of ~3.7V…that means this is the normal operating voltage. It is hardly a failed battery when it is at 3.8V. A fully charged battery will be ~4.2V. The phone will operate with the battery as low as ~3.1V. Voltage is not the proper way to determine if the battery needs replacement or not. The proper way to do it is to look at the actual design capacity of the battery, via software tools like coconutBattery or 3uTools. There are also some hardware solutions available that do the same thing. You are essentially reading the data off the gas gauge IC inside the battery pack.

The challenge nowadays is that most replacement batteries have sketchy readings from the gas gauge. I ordered one batch of batteries from a supplier and noticed they all had the same serial number and design capacity specs…dubious at best.

The other option is to physically test the battery against a dummy load. I certainly wouldn’t do this on every battery but it’s a great way of spot checking a supplier or a particularly frustrating repair where you need to be certain the battery is good (despite good data from the gas gauge).

This is a good/new battery running at 0.1C. Note how the majority of the time, the battery is operating around 3.7V (hence the nominal rating) and it lasts around 8 hours.

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This is a dead/dying battery (23% of design capacity). It also operates around 3.7V but only lasts 48 minutes before hitting the 3V threshold.

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You may have noticed the bounce back effect in this second chart. Once the battery hits 3V, the load is cut and you can see the battery voltage bounce back to ~3.8V. The battery is fully depleted yet still shows 3.8V without a load (such as a multimeter).

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I am not sure how I can explain the policy any more, if it tests over the rating listed on the battery it is replaced. Thanks for the explanation, I do understand capacity is what should be inspected and not voltage. At the most basic diagnosis of battery life we charge the customers phone to 100% then run a full screen movie on YouTube with the brightness and volume maxed out. We time it then run the same video with a new battery charged to 100% and base it off that.

IMO a better way of doing it (without software) would be to use a USB multimeter that counts the mA pass-through during charging. Drain their battery in question to 0% and charge it through the USB multimeter and see if it fills the rated capacity before stopping. Would this be accurate?


I used to repair phones at a Batteries Plus Bulbs store, so I do have decent knowledge of how batteries operate. From the standpoint of a lead acid starting battery for a car (cranking amps) we would load test the battery at room temperature and watch for a voltage drop when the correct load is applied. If the voltage dropped below 11.5v at room temperature with the rated CCA load being applied the battery was diagnosed as bad but as you said the voltage came back up after the load was removed from the battery. Lithium batteries do not necessarily have a cranking amp rating but they are still required to supply a peak load.


That's what you can see in my graphs. They were done with an integrated USB meter and load. You can then match the actual mAh the battery gave against what it is theoretically designed for. Of course, it's impossible to know what conditions Apple uses to test the batteries so this is the best you can do.

Running a device at full brightness is a good way to do it without having to access the battery. I do this often when I'm unsure about the condition of the battery.


Integrated USB meter? You mean the in-line style? I was thinking about playing with those DC power supply break out leads with all the different iPhone battery Lego connectors on them. Have the end that usually has bananna plugs connect to a multimeter and the battery in question, so you can monitor the voltage the battery is supplying to the phone under a load. This may be the ultimate way of doing it; being able to monitor the battery voltage as its being used.

I should look into getting some diagnostic hardware and PC software.


This is what I used to chart the graphs. Ideally you would want to do a contant power graph, not constant current. The company manufactures a CP device but it is more expensive. This little device is pretty darned good and the only one I found (at the time) that did data logging.


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HI, you will find that the Kaisi board is not a safe way to charge a battey and has no safe way to charge.

Please take a look at the below links to get the best answer.

Please let me know if you need further assistance.

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Wow I had no idea it was not a safe way of charging, unfortunately I do not have the time to read that entire article it appears a bit over my head.


Sure thing! The Mods that we have made will be released over the world in next few weeks, it will allow you charge and discharge you batteries at a safe state and leave them at 50% for safe storage.


Your links go to a page of products, can you tell me which is the one used for safely charging and discharging batterys? Ive also never known Kasis was not safe.. also how do you discharge on your product?


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Nate Thibault zal eeuwig dankbaar zijn.

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