Battery Charging Guide / Info

Li-ion Battery Charging > Mobile phones > Fairphone

Battery or Cell: APPENDIX 1
Charging to 100% APPENDIX 2
Charging slowly, Charging, Charging rapidly: APPENDIX 3

There are up to six items involved in charging a phone as follows:-

1. The source
This can be ‘high voltage mains’, DC from Solar panels, a computer or a Power Brick especially designed for topping up mobiles: as examples

2. The supply
In the case of mains first came the dumb mains charger. They would convert mains 115V∿AC or 230V∿AC to a suitable 5V output and usually had a fixed cable. (My Nokia charger output 5.3V at 500mA). Whereas they used to have propreitory plugs to the phone these became more commonly micro USB.

In the case of a computer some provide a 5V output with a variance, older USB 2 versions could supply up to 500mA and the updated USB 3 up to 900mA. These supplies invariably came from the USB A type socket whereas as the USB C connector is more common then these connectors can also be enabled with either USB 2 or USB 3 protocols. Simple info on USB 2 and USB 3 differences

Solar supplies are usually via a converter that are attached to a battery of often 12V sometimes 24V.

As in a car cigarette-lighter-socket adapter you may find a USBA and or a USBC socket. These sockets can have a range of voltage options and can provide up to 5000mA current

Then we have the ‘smart’ charger. This only works with a ‘smart’ circuit in the phone and a suitable cable.

The smart charger can be the aforementioned 12v adapter or more commonly a mains charger.

These smart options use, most often, proprietary protocols and are not compatible. Saying that, many chargers are capable of communicating with multiple protocols. Two major ‘smart’ protocols are (QC and PD) the Quick Charge by Qualcomm and the Power Delivery more often associated with laptops. Each having their own variances. More recently there is the PPS Programable Power Supply which is an attempt to bring things together.

3. Not all cables are equal.
Some are wired differently and some even have a chip in them to say they can handle 100w. I’ll not elaborate of the wiring options here, yet.

4. The smart phone.
The ‘smart’ phone can ‘negotiate’ with a smart charger to supply a high voltage. The Fairphone uses Qualcomm chips on the core module to do this.
Note that a battery requires around a max of 4.4V (Fairphone) to be fully charged and an input of 5V would suffice.

However many cables have such fine wires that can only handle 500mA or 1A safely and so charging could be slow. Hence if there is no communication between the phone and the supply the phone can fall back to 5v and limit the current to 500mA.

However if the phone sees the charger can supply 15v and 1A and not burn out the cable it can draw 15W in an hour rather that 5w (5V x 1A) so charging the battery ‘rapidly’

5. Battery circuit
The battery has a circuit to protect against ‘overcharging’ so it that if it is working the theory is there is a maximum voltage that the battery can be charged to irrespective of the supply and the phone’s arrangements.

6. The battery
The term battery means a collection of cells in parallel or in series, though is also commonly used when referring to single cells.

In the case of Li-ion batteries where there are multiple cells the battery has an electronic circuit to equalise each cell so that some do not get overcharged whilst others undercharged by a single input voltage, from the, in this case, the phone’s management.

I have no idea if the Fairphone batteries are single cell or not. I will ask. See APPENDIX 1

The battery has it’s own physical limits which are not usually approached.

It may well be the case that for ‘longevity’ of the battery, the phone will state the battery is fully charged 100% when it is in fact only 90%. This stops overcharging.

And so we have this notion of overcharging.

Overcharging is a very subjective issue and comes down to battery design. There is a designed and theoretical maximum voltage that a battery can be subjected to over a period of time.

So it is possible to overcharge a battery no matter how carefully all the precautions are taken.

Some overcharging or let’s say prolonged charging and topping-up may degrade the battery’s longevity, a high and quick overcharging is not only likely to cause failure but be a physical hazard and result in fire or explosion.

So ensure the battery never gets very warm.

And note Fairphone suggest so as not to overcharge the battery in the sense that fully charging frequently can shorten it’s life to limit the charge to 90% for example. Maybe the use of the word overcharge is an issue and so it could be said that undercharging a battery could be seen as valid but I think not.

Charging a battery to the phone manufacturer’s stated level is termed 100% whether that is overcharged or undercharged can never be ascertained. Consequently the safe side would be to treat full (100%) as over rather than under. Terminology is at best vague and worse a distraction.


Having a parallel combination of cells is also not useful because of the additional complication of balancing the cell voltages. A multi cell system would require cell voltage balancing for the sake of safety and longevity of the cells. batteries - How many battery cells in a smartphone? - Electrical Engineering Stack Exchange

Late 2017 update folks, The iPhone X packs in two cells. They’ve probably done this for better space management and have chosen to integrate the balancing circuitry as a trade-off for this. Check this link -


Charging a Li-ion battery is a bit of a mystery, unlike Lead Acid batteries where the specific gravity of the electrolyte can be measured the ‘full’ charge of an Li-ion battery is a mix of voltage and current measurements.

For example if the maximum Voltage is designed at 4.5V the battery itself may limit it to 4.4V. When the battery has reached this voltage the current can be monitored and for example when the current is 45mA it may stop charging and indicate it is fully charged. It is not, but for the end user it is.

The issue that is sometimes discussed is how often should a battery be charged to ‘full’ the not really 100%

The batteries are designed to be ‘fully’ charged and Fariphone give a two year warranty on the battery, so they are not worried if the user charges to 100% as shown by the phone’s monitoring system

However charging a battery cause stress to the battery so it is arguable that the battery may ‘live’ longer if it suffers less stress, hence Fairphone’s advice.

If you store your battery/device over six months, make sure to charge it between 50% and 80% every six months.

Note there is no suggestion to store a battery at 100% as it is unnecessarily stressful.

For a ‘power’ user it may well be the only viable option to charge the phone to 100% ~ this is not a good or bad idea as some like to think, but a preference.

we recommend to keep the charge of your battery between 80% and 20% at all times to keep it longer.

Batteries are never charged completely they are either being charged to a level set by the manufacturer of the device that uses the battery, in this case Fairphone or they are discharging, albeit maybe at a very low discharge rate especially if removed from the device.

So for some checking the battery status to ensure it doesn’t go beyond what the user decides is not a scare tactic. Some people have lower limits that those set by device manufactures.


Being written :slight_smile:

Whereas the terms are understandable the functions are not.

The lack of clarity is two fold
a) When do each of this kick in and
b) What range of charging does each have.

Such information would help in assessing the use of some chargers. So here are some basics.

It would re reasonable to assume that if the phone cannot communicate with the charger it may just say ‘Charging’ However I have for 10 months used a dump charger: a 12v to 5V adapter.

Not withstanding that there is a different with cables, I generally use the FP cable, one that I see is not available in the shop.

The problem I have is that charging is very inconsistent. I very rarely have Charging rapidly. Most of the time it just says ‘Charging’ and occasionally will say ‘Charging slowly’

There are 'stories that when the phone reaches 90% it will drop to charging slowly, but this doesn’t happen with my dumb charger although no doubt the charging rate drops: I can tell from how many minutes are left.

Maybe as this ‘dumb’ charger only supplies 5V the phone doesn’t see the need to inform that it’s ‘Charging slowly’.

NOTE: Using the Settings > Battery > ⋮ > Battery usage

The battery usage is reset each time the battery is fully charged. That seems to be around 90% on my phone, presumably where any smart charger will have it’s voltage restrained.

Charging rapidly Example 1.

Usually I charge before the battery gets below 30% but last night/this morning I let the battery get to 5% and then decided to charge to 100%.

  • The battery although saying charging rapidly said 3 hours to go, which is definelty not rapid.
    At 57% it still says ‘Charging rapidly’ with 1h 45m to go,
  • At 99% It said Charging rapidly until in said ‘Charged’ 100% There’s no doubt it sped up when it reached 54% and slowed down when it reached 96% but without repeated monitoring that would not be known.
  • Overall this took 5hrs, so not what I would call ‘Rapid’ with the caveat that this was from 5%. Usually it is quicker per percentage.

It seems the charge level of the battery greatly influenences the rate of charge

Charging Rapidly Screenshots

Above you will note that with a battery at 57% there was 105min to full charge. Given the battery is over 20 months old that means the battery is likely somewhat less than the 3000mA is was when new.

Even so 105 min to do 43% equate to ovcer 4hr to charge at that rate.

At 600mA a new battery of 3000mA could charge in 5 hours so 4 hours could be that the battery is about 80% good.

These are only calculations not facts.

The point is that ‘Charging rapidly’ isn’t the same as the battery is charging quickly.

It is a mysterious function whereby the phone states it is charging rapidly when clearly it is not.

Before I show two images of the phone ‘Charging rapidly’ I would like to mention that the notification ‘Charging rapidly’ can arise whether of not I am using a QC3 rated charger or a dump 12V to 5V old car charger and totaly inconsistent at that.

I did ask fairphone for soem technical info but after months of ineffective responses I gave up enquiring.

Here are to images of ‘Charging rapidly’ with a short look at the detail

Note that in the later image although the phone had more charge the time to full charge was longer.

Some detailed view on the charging chemistry and charging levels


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