How to prevent brightness from going to full when the battery low popup appears? Whenever the "battery low" popup appears in my tablet, the brightness goes to full. This makes no sense because the brightness should be decreased to the minimum instead of going to the maximum, as battery is low. This is also annoying as I have to lower the brightness.

I've looked in the settings to disable this but found no such option.

So, How do I prevent brightness from going 100% when the battery low popup appears?

I am running Android Kitkat 4.4.2 and my tablet is not rooted.
Automation is the preferred option, or rather only option in this case, since Android OS does not offer any settings for requirements quoted.

Many apps are available. I prefer using MacroDroid , since it is free (upto 5 macros) and easy to learn. 

MacroDroid creates and runs Macros to automate


  A macro consists of the following (elaborating on app help):
  
  Trigger
  
  Event(s) occurring on the device (e.g incoming SMS, headphones inserted). Multiple triggers are evaluated to logical (OR)- meaning, any of the trigger conditions met would fire macro
  
  Actions
  
  An action that the device can perform (e.g. set wallpaper, take picture)
  
  Constraints
  
  A constraint that must be satisfied for the trigger to fire (e.g. day of week, battery level). Multiple constraints are evaluated to logical (AND)- meaning, all  the constraints must be satisfied to fire trigger


Notes on solution offered  


Tested on KitKat. I don't visualise any issues with higher Android versions
This cannot "read" when the low battery level indication comes up, but for this macro assuming it to be 15 %. You can see the battery level in your tablet and accordingly tweak the macro
Doesn't require root
This solution does not address Android system explanation for high/low Brightness and  how they are activated


System Settings


Do not Greenify MacroDroid and exclude it from task killers, if you use them.
Enable MacroDroid in "Auto Protect"(Huawei phones) or "Stamina Mode" (Sony phones or "Power Nap" (Stamina Mode Xposed module for non Sony devices). Also, if you update to Marshmallow in the future, exclude MacroDroid from Doze. Refer this: Is there a way to exclude an app from Doze?


These features prevent app(s) to be active when the device is not awake, conserving battery. May not be pertinent to your phone but adding this as a general precaution.


Enable MacroDroid in accessibility settings and also allow it as device administrator in security settings.
For Lollipop, enable notification access from notification settings




tl;dr:  Your macro would look like this

Trigger:

Battery Level &rarr; decreases to &rarr; (choose percentage by sliding scale or 15 %)

Actions: 


Brightness &rarr;0 (Choose On sliding scale- doesn't require root)
Wait before next action &rarr; set to 10 seconds (recommended to separate previous and next actions ensuring both happen)
Dim Screen &rarr;Dimmer On &rarr; 10% (Choose On sliding scale- doesn't require root, if the earlier action is not good enough for you -    this is akin to "screen filter" apps like Darker)


Constraints:

None  (Macro always runs)



Testing Macro

Name and save the macro and from 3 button menu on right side


Test Actions:  To see how macro behaves at each action without reference to trigger/constraint conditions
Test Macro:  To see how macro behaves as expected
( with reference to trigger/action/constraints, that is, macro as a whole)


Trouble shooting

Macro doesn't run at all- In most cases, it is due to correct system settings not being applied. To verify this, from the 3 button help option on the main app interface select System Log and see if your macro had run when it was triggered. If your macro name doesn't figure, recheck system settings