Using two batteries interchangeably

I have a second battery which I ordered when I had huge problems with my first FP2.
The problem was not the battery but after my first FP2 died I now have 2 batteries.

And because the battery drains within 2 hours when playing games, I always kept both batteries charged and with me so I could swap them if needed.

My problem is that the phone always has difficulties estimating the remaining charge level of the battery when playing games. The % can drop from 15% (the warning) to 0% within 5 minutes.
I looked up how a phone measures the charge capacity and now my guess is that phones are not programmed to handle two or more batteries interchangeably.
So what should I do? Only use one battery and a battery pack instead?

Another question, which might need another thread:
Could I somehow run the phone without battery when playing games? I assume that discharging and charging at the same time for hours does not do any good for the battery.
Once the battery fell out while the phone was connected to a charger and it kept running (I put the battery back quickly, so I cannot say how long it would have run) but when I tried again later by removing the battery it shut down immediately.

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Hi Lachi - I’ve also been using two batteries this weekend (whilst travelling, so couldn’t always charge from mains). Having read your post I now wonder if it was swopping between the two that caused both batteries to suddenly drain very fast this morning (and phone got v hot), even on flight mode.
They then wouldn’t recharge either, but looks as if one of them’s now recharging, fingers crossed…
Would be good to hear if others have had similar issues.

I don’t have problems charging my two batteries and I don’t think they are hot (without playing a game).

But the phone does act strangely sometimes. Today, for example, I was charging both batteries after each other:
I charged battery 1 until 100%, then I turned off the phone, removed the USB cable and removed the battery 1.
After 3 minutes I put battery 2 and turned the phone back on.
After fully charging battery 2 I turned the phone off again and removed the cable and battery 2.
After another minute I put battery 1 back in and started the phone.
Now the phone showed a charging level of 83% for battery 1. So I connected to the charger again but after 30 seconds the charging level went up to 100%.

It would be nice if one could use a phone directly from the power supply, without using a battery. But for as far as I know, there are no such phones. Only laptops allow this.

I also have two batteries since my phone purchase >2 years ago. I swap them by occasion to have a more or less even wear.

Yes, the estimation of the power level is not very accurate after having swapped the batteries. This should be corrected after the first full charge, but up to now I never had a massive offset. Only a few %. A re-calibration is possible it´s explained in the #batteryguide but should not be done after every exchange. If you replace the batteries on a regular base due to heavy gaming maybe once per month should suffice. I have done it only twice by now. The first time I had an realistic offset of about 20%. The phone showed 0% but ran nearly 25min. longer.
When I change them regularly I keep them at about 80%. So after this the offset is not so big.
For your need a battery pack may be beneficial. But don´t forget your spare battery somewhere in an abandoned place. And free the power once in a while.

That´s not unusual. Depending on the use it may keep up for a while, but quickly dropping when being already beneath the last 20% is also possible.

Doesn´t work with FP2. @MathiasVA also states notebooks allow this, but I cannot explain why smartphones (maybe not all) does not.

Well you will have many charge cycles coming up. If the battery is of decent quality you have some about 500-1000. No one can tell for sure how long it will
keep its full capacity until it drops to 80%, starts to swell or won´t charge at all.
But that´s the usual wear which cannot be avoided, not even by not using it.
To compensate the time factor I would use it as you need and once in a while swap and fully charge for an initial closer estimation. That way you may keep both batteries for a long time in a healthy state.


None of this type up to now.
Each reboot gets the phone heating up for some time until all processes are
up and running again, hence the battery may lose a few % charge. You can noticeably drain your battery with a limited amount of reboots.
Hence OS updates require a minimum charge level or being plugged prior to start.

Thanks to all.
I will live with the inaccurate power estimation and just use a battery pack.

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