Charging a smartphone battery while using it

Question

While this question pertains to smartphone , it is being asked from purely an electrical engineering view (My electrical knowledge is very basic)

Trying to understand if charging a cell phone and using it is recommended or not, I came across this Charging Li Ion battery

Quoting extracts (emphasis mine)

portable devices sit in a charge cradle in the on position. The current drawn through the device is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic loads while charging because it induces mini-cycles, but this cannot always be avoided...."

A portable device should be turned off during charge. This allows the battery to reach the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low by drawing a leakage current. A battery may be fully charged, but the prevailing conditions will prompt a continued charge, causing stress."

I wanted to verify this by testing to the extent possible with limited means. I ran two tests.

For measurement of voltage/Current used an app 3C Toolbox, which gives measurement at every 1% change in both tabular and graph form

First test was normal charging in air plane mode. Had to keep the phone on to run the app

Second test, was to charge the phone while simulating usage. Instead of actual usage, kept screen display on at 50% brightness to simulate usage load, since this would give a steady load and had read elsewhere that this would approximate a 2G data download load

I wanted to compare with the graph quoted in the linked article pasted below

Test results for voltage and current are pasted below. The first graph on the left side is of first test and next is of second test (pale gold line at bottom shows screen on status)

Charging Time. Identical in both cases -121 minutes

Voltage

Current

Temperature

Edit Notes

I have edited the question, making it more focused to validate my interpretations of the results of test. In this context :

a) I fully agree that this is not a rigorous scientific experiment

b). Battery University talks of effects observed while charging with device on. Here the comparison from my tests, is not between charging while device switched "off" and "on". It is a comparison between charging while the device is on with " less " load and " more" load (device on with screen "off " and device on with screen "on at 50% brightness")

Having made these points, I believe that these tests offer indicative trends and is reasonable to compare with Battery University and draw conclusions

Inferences

1. Voltage. This offers the most striking contrast.

a). While the time taken to reach maximum voltage and voltage levels are nearly same, the voltage graph shows steep ramp up compared to the first. This means that the topping up of charge is gradual in the first case, since more time is spent at various voltages. This translates to longer battery life per cycle (assuming equal discharge conditions applied to both cases).

b). Battery University says

A parasitic load confuses the charger by depressing the battery voltage....,

this can be observed in the second case more prominently and confirms the behaviour

2. Current.

a). The current graph in the second graph, exhibits a pronounced saw tooth shape before it drops off. This corresponds to mini cycles caused by parasitic load as mentioned by Battery University

The current drawn through the device is called the parasitic load and can distort the charge cycle. Battery manufacturers advise against parasitic loads while charging because it induces mini-cycles, ....

b). Further, Battery University statement below cannot be established, since in both cases, the battery is being charged while in " on" condition and measured drop is nearly the same when you compare the maximum and minimum

A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low by drawing a leakage current.

3. Temperature. The battery temperature in second case is marginally higher by 2°C and while it is not significant, it can be argued that it is not desirable for battery, since increased internal temperature while charging leads to more internal stress.

4. Charging Time. Same in both cases and the charger having a limited capability to supply voltage or current, Would imply that there has to be a trade-off between quality of charging with more load, as is evident from the graphs above

Conclusion

Inferences above are in line with Battery University and consequently one can conclude that charging battery, while device is switched "on "or "in use" is NOT a good practice. This is further supplemented by best practices shared and amplified by @ericnutsch (thanks) here.

Question

Seeking anwers for confirmation or negation of conclusion highlighted above (backed by technical sources and citations). Additional inputs on charging methodology implemented by major OEM cell manufacturers to cater for "charge while in use", would be appreciated

Please ask if any other information can be provided apart from above and cell phone is Honor 6, with 3100 mAh battery.OEM wall charger of 2A used

Answer 1

First of all it is highly unlikely that the one would find public information of major OEM cell phone manufactures battery charging methodology back by technical source and citations as this would be a breach of confidentiality. Having read your post and references I can safely assume that you have some understanding of rechargeable batteries and related charging methodologies. Also source referenced in your post are very credible.

Also in modern rechargeable battery systems don't directly charge a rechargeable batteries as per the reference in the post. Custom silicon IC do charge batteries as per the diagram in the above post.

As per your own reference a battery charging system can be designed such that use of the mobile device and battery changing can safely occur simultaneously.

_{This image was extracted from Microchip Application Note link cited both by @beeshyams and @ericnutsch.}

Reading through your post I believe you have done a good top down analysis of the workings of rechargeable batteries and battery charging system. Thus I have described below a bottom up engineering design approach for a rechargeable battery system for mobile devices used in enterprise and medical application. It is my belief that this would help you in understand of rechargeable battery systems.

In both the cases the customer/consumer was seeking a mobile device that would guarantee more than 8 hours of usage without recharging. One application was primary at room temperature but the other application had a wider temperature requirements. Also note that this process is fairly dated and some of the applications has been already been sunsetted. The high level steps were

• Select a rechargeable battery vendor
• Determine the appropriate battery charging circuit
• Design and Test both hardware and software for the mobile devices per the customer requirements
• Furnish parametric data to validate customer/consumer requirements

Select a rechargeable battery vendor

Many vendors were evaluated including vendors such as Maxwell, Sanyo and Sony. Although all vendors offered similar batteries at high level, parametrically particularly at extreme temperatures some venders had superior performances. Test systems from Maccor and Cadex were used for battery parametric testing.

Determine the appropriate battery charging circuit

Texas Instrument and Microchip both offers very good battery charging silicon and support. I am sure other vendors offer superior battery changing silicon unfortunately I don’t have much experience with other vendors

Design and Test both hardware and software for the mobile devices per the customer requirements

This was very interesting and challenging phase, because generating, storing and displaying parametric data as per the above images on the question was very difficult particularly for extreme temperatures.

Furnish parametric data to validate customer/consumer requirements

I suggest you refer to Maccor, Cadex, Maxell and Sony information device level parametric data. Also I suggest you take a look at Portable Rechargeable Battery Association (PRBA) and International lithium battery regulations where there is a better chance of finding public information.

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References:

• Battery Management Solutions
• Is battery-charge-stop-at-XX-percent circuitry not cheap?
• What is the minimum current required to charge a smartphone battery?
• Battery charging, management with the Fuel Tank BoosterPack

Answer 2

I am not familiar enough with your tests and your data to draw any conclusions from it. Perhaps if you infer your own conclusions citing specific parts of your data I would be able to follow better and see if your conclusions are sound. I am not sure if the data you are seeing is significant or just noise in the testing process. I am also not an EE so EEs feel free to correct me.

Typically a modern battery charging/power system has functionality to charge the battery, pull from the battery, and draw from line power directly when available(5v usb in this case). This allows the battery to charge according to what is best for its chemistry. No discharge on the battery occurs until it is disconnected from line power.

This link describes it much better than I can: Designing A Li-Ion Battery Charger and Load Sharing System With Microchip’s Stand-Alone Li-Ion Battery Charge Management Controller

So no, it does not harm the battery to charge and use it simultaneously. I believe that this is a common perception because the phone may operate much warmer than it usually does. This however, is due to the fact that both the battery and electronics are giving of peak amounts of heat; not because damage is being done.

Older lead acid systems like on older cars (not sure about the new ones) don't do this, and just put the battery right on the bus. Cars don't have to hold a very close voltage tolerance, and lead acid is very forgiving so the system works fine. They could however increase battery life if they managed it in the controlled way as mentioned above.

Edit:
I have re-read your question and Mahendra Gunawardena's answer. The battery charging schematic in the link I provided, and cited in Mahendra's answer is evidence that the best practice is to use a charging chip that correctly handles use and charging simultaneously. Companies like Samsung, HTC, Motorola, Apple, and Google, meet or exceed best practice. I can not provide you an electrical schematic of one of these phones, but by logical deduction I can assure you that if a superior solution exists, they are using it. Consequently, I reject your hypothesis that "charging [a cell phone] battery, while [the] device is switched "on "or "in use" is NOT a good practice."

Also, I think I have found your misunderstanding on the voltage: In your voltage graphs, you arrived at 4335mV and 4250mV. The starting points were 3930mV and 3981mV respectively. Note that your axis is not the same on each graph and that the slope of each voltage graph is basically the same.

While your battery university link does have a nice collection of resources; their information is not up to date. If the battery and load are on the same bus, yes what they state is true and it will harm the battery over time, but modern electronics do not do it this way anymore; as seen in the microchip electrical schematic. Also if it was occurring, the small amount of parasitic load from the phone being on in airplane mode would have nearly the same negative effect as a larger load.

To dive into the voltage a bit further; there is no harm in the final charge voltages being slightly different either. It is also likely that the chip controlling the change targeted a different final voltage based on temperature compensation.

To trust this data you would have to preform this test tens of times and analyse your data statistically. Then you would need to graph it vs other variables like temperature to check if the chip was compensating or not. End of the day, your measurement here is lost in the noise of many other factors.

The current graph is inconclusive because we have no idea if that means load draw(just the phone electronics) or line draw (battery and load). We also dont know how they are measuring this.

I have already reviewed that the temperature would be increased because the usage also produces heat that adds to the total. This heat is not an issue for the small differences seen; like your 2degC for example.

Answer 3

Based on the answers here it shows that interpretation of my results was wrong.

This was independently validated and supported by Bruce Huang of Battery University. Main points from him were

1. Parasitic Load would not delay current drop indefinitely, it does do momentarily.
2. Keeping the screen on at 50% load does not create a significant load to create noticeable parasitic load
3. Charging time may vary depending on the load

Full text of his reply and my answer based on his and inputs obtained from this answer.

I would still hope to obtain some inputs on OEM implementation of charging

Answer 4

mobile technology,

1.By pass mode is not available,

2. Your battery have cycle, Charging and Discharging, So need to chargeable FULL, In emergency use Battery Bank,

3. Don't charge cont, Full Battery 95%, 85%,92%, Wait after dry to minmum 30 to 20%, your battery life will be more ( Practical Hence proved )

4. In case you are using in battery charging condition, Profit for mobile and Battery companies ( point 3.), 4.1 OEM please refer about OEM, They are not to be R&D / Own brand manufactures. The are branding company that all.

   I never recommend to charge within use.