FP4 Battery life

If this is useful to anyone running an alternative OS in which the charging control option is available:

Apparently the control algorithm has a hysteresis of 3% - meaning if you set a charge limit of 80%, it will wait until the charge drops to 77% before turning the charger back on. So if you really insist on having a guaranteed 80% charge when you unplug, set the limit to 83%.

Also, it slow-charges around the limit, meaning it behaves exactly like it would at 100%, even if the battery is capable of charging faster at the limit you set. As a result, it takes rather a long time to get to 80%. It’s perfect for leaving the phone on the charger overnight, but if you need a quick recharge during the day and you’re in a hurry, remember to turn the charging control off.


Oooh, pure geek bait! You have a USB Ampere-meter? Where do you find such a thing? (Want! Want! Want!) :rofl:

I stand corrected about the charging management. That been said apparently the OS has some control nevertheless, which doesn’t surprise me because that charging chip needs to be adaptable to all the different batteries and phones, all with differing requirements, and the easiest (cheapest) way would be to offload a part of the control to software.
Now how does it charge when the phone is off? Well, I guess it isn’t really totally “off” while charging, it must load some minimal OS, after all it does control the display and all.

Ah well, I lied a little :slight_smile:

I have several very nifty XTAR P2BS powerbanks that use a pair of 18650, 20700 or 21700 Li-Ion cells (and I have a million of those lying around from back when I was a heavy vaper). I use the powerbanks to test USB-C PD chargers, USB-A QC and non-QC devices, as well as cables. Here’s how:

  • The P2BS charges off USB-C PD. so if I want to test a USB-C charger, I plop depleted Li-Ion cells in the powerbank, connect it to the charger with my best USB-C cable, and the powerbank will display in real-time the voltage it negotiates with the charger and the amperage it draws from it (up to 18W, which is the rated limit of the powerbank). Of course it will tell me pretty quickly if the USB-C charger isn’t PD-compatible. Likewise, if I want to test a USB-C table, I plop dead Li-Ion cells, use my best charger and test the unknown cable instead.

  • The P2BS supplies power to either a USB-C PD-capable device (up to 18/20W), a USB-A QC-capable device or a USB-A 10W device. To test the device, I deplete its battery then connect it to the powerbank with my best USB-C or USB-A cable and again, the powerbank will show which maximum voltage / amperage it supplies to the device. Likewise, to test a cable, I use the most capable of my USB-C or USB-A device with dead batteries and connect it to the unknown cable. Of course, it you watch the powerbank’s display as the device nears 100%, it will also show you how the voltage / amperage evolves as the power draw drops.

So, it’s not a dedicated ammeter, but it’s plenty good enough to test my gear. And when I’m done, it’s also a useful powerbank :slight_smile:

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Yes :slight_smile: it doesn’t count individual electrons, but waves of them.

Wow! I bought a spare battery for my FP4 the other day - you know, in case they become unavailable some day… I plopped it into the phone to give it a full charge / discharge cycle and it gets 3 full days of normal usage!

The battery that came with the phone - supposedly identical - only got a hair under than 2 days.

Crazy difference!

I have just got a new FP4 so have no experience to share yet but am looking for advice/input - please do say if I should start another thread with my question which is the following.
What thoughts do any of you have about best charging practice for optimising battery life?

I read various things when considering this for my FP2, such as not letting the battery get below 40%/20% & not charging much beyond 80%/90% : different users had different charging boundaries.

So, I’d love thoughts regarding the FP4…
with many thanks,

Ah, I’ve just seen that you @anon9989719 don’t let the battery go below 20% and not above 80% - have I understood that correctly?

I use the app AccuBattery to limit the charge to 85%. I get a sound signal when 85% is reached. If I don’t stop the charging, then the charging will go on. So very rarely my phone is charged above 85%.
I start charging every morning and the phone is then mostly between 25 and 35%.

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Perhaps it’s worth mentioning again that if you install CalyxOS on the Fairphone 4, the Android charging control is enabled:

Just set it to whatever maximum you like and it’ll stop charging all on its own. Better: once charged, it’ll (mostly) power off the USB plug instead of yo-yoing the charge level.

Thanks so much for this @Lidwien, I’ve now installed AccuBattery too & set upper limit to 85% :smiley:

Hi everyone, I bought the fairphone 4 in June 2023 but I have the impression that the battery lasts very little.
today at 2pm it was already at 15% after an average use.
Does anyone know if this is normal for this model or if there is something wrong.
Thank you


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The use time on my brand new FP4 was 23 hours with the stock Android OS and 44 hours with CalyxOS. I believe the difference is solely due to CalyxOS not snitching on you and sending data to Google all days long, letting the phone sleep longer.

Better: I got a replacement battery the other day and it appears to have a significantly higher capacity than the original one, giving me almost 3 days of use.

Bear in mind that it is light use. I don’t spend my days gaming or doing Facebook. Still, it’s always exactly the same usage pattern, so the comparison is meaningful.

First check your battery if it is swollen. Do the test shown in this video from Fairphone.
Then you can try a kickstart to reset the software in the battery.

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Some people have also noticed a higher battery consumption when using 5G. It depends on your carrier though, I for instance use 5G and my battery lasts the normal time.

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Been a while since I posted on this topic.

For the last few months, my battery life has drastically reduced on LOS 20.
No changes were made whatsoever in terms of installed apps or phone usage.
90% of my apps have their battery setting set to “limited”.

Seems to be consequential to an LOS 20 update but I wouldn’t be able to track which one.
Has anyone observed similar issue ?

Yes I have a similar experience. In the early days of LOS 20 on the FP4 I got 10+ days of standby usage with a fully charged battery (no Wifi/mobile/bluetooth connection, only 4G voice service, dual SIM).

From one day to another (and since then) I only get max. 2 days of standby usage, even without using the phone at all. No apps or settings were changed AFAIR, and the battery usage screen does not show any apps (the “highest” usage comes from “Mobile network”, but only 2%)

The only bug report I found last time I checked (2 months ago) regarding high battery usage was this one:

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In the last days I noticed quite a high battery usage on my FP4 (A13): Today, in 2 hours I lost 25% of battery! I could track it down to 33% of this to “Cellular Connectivity”. I already switched to 4G as my plan does not cover 5G anyway.
Did someone else encounter such a battery drain?


I had to load my phone more often the last 2-3 days. But I thought, it might be because of increased usage. No 5G in my contract, either. O2 mobile network, Germany.

Here it is O2 as well. I use O2 via my internet provider M-Net. Resellers in O2 do not get 5G, yet.
So this might be related to changes on the providrer’s end

Same here. T-Mobile Austria. From one day to the other it won’t last eight hours. It’s getting hot, especially in the upper left corner. And all is going to “Mobilfunknetz”.
Support told me to switch off NFC, but that didn’t help.

I also bought my FP4 around that time, and from one day to the other it’s draining within 8 hours (it lasted 48 hours originally).
Did you contact FP support?