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# Added a second battery to my tablet

#### Pssdof

Dec 26, 2017
2
I have succeeded in installing second battery in my tablet but it still has the same life time. Is there a battery app that might make my tablet know it has more to charge? I had two of the exact same tablets brand new kid stepped on one so I used exact same battery in parallel.

#### dave9

Mar 5, 2017
1,188
AFAIK that would be a manufacturer and model specific app while you didn't mention your man./model. I'd do a web search for [model name] recalibrate battery.

Dec 26, 2017
2
Thank u ill try

Jan 4, 2018
11
which model?

#### HellasTechn

Apr 14, 2013
1,571
If you have the batteries connected in parallel then it does not make sense to have the same battery life.

If in parallel then the batteries have to be of the same mah rating, then in the same charge level e.g. both empty before you connect them on the mainboard. Then charge them to full capacity and again observe battery life. it should be roughly double if both batteries are not too old.

#### dave9

Mar 5, 2017
1,188
^ It makes sense when the device is calibrated to a specific battery capacity and has a background app that shuts it down at a certain % remaining charge. In such cases when you "upgrade" the battery you need a method to recalibrate for the new capacity, method meaning sometimes there is an app feature, or less obvious method that could be researched.

#### HellasTechn

Apr 14, 2013
1,571
It makes sense when the device is calibrated to a specific battery capacity and has a background app that shuts it down at a certain % remaining charge.

I understand your point. The question now is, how the device sense remain battery percentage ?

Most tablets calculate remaining battery percentage based on battery voltage. The app on such device will not read that the battery is say at 100% if voltage is not at 4.2 Volts. Now two batteries of same capacity and same state of charge will not give the voltage of 4.2 if they do not charge at 100%.

Does it make sense ?

#### dave9

Mar 5, 2017
1,188
^ Sure, but if it displays battery full at 4.2V, doubling battery capacity does not change that. IF it has to be calibrated to correctly display remaining charge once it has begun to discharge, doubling capacity does change that.

Apparently it is not the case that all tablets determine capacity by a voltage measurement alone. I wonder if this is due to issues like changing load, that it might sip power in a sleep state but rapidly consume it playing a game or video, causing a temporary voltage depression, but they don't want it shutting off, dimming the display, or other power saving strategies prematurely.

Battery calibration is a thing but we have no info about whether Pssdof's tablet does this and/or if any attempt had been made to calibrate it.

#### HellasTechn

Apr 14, 2013
1,571
I hear ya but still i am not sure...

#### dave9

Mar 5, 2017
1,188
^ That the topic exists at all should be evidence enough, unless Pssdof is just making up fiction or misunderstanding how to check the battery life.

#### hardwaylearn

Jul 6, 2018
6
my tablet batt failed so I used wirres to connect to 18650 outside which i charge separately. The tablet shuts down low batt at 3.7v, so is set too high. I use 18650,s in portable radio(1) & radio runs till batt goes to 2.3v. I recharge with no worries.

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