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If you have this feature on the battery menu, regardless of the Samsung model, be it phone or tablet, it adjusts the battery charge scale, so "real" 85% shows as 100% on the battery charge icon and also turns off charging when its reached, but only if Android is booted.
If you reset it back to normal, that is 'protect battery' is off, so 100% = real 100%, you may have to recharge the tablet back up to the real 100% to insure its calibrated. You can follow this by checking the actual battery voltage with any good charging app or Zoran's 'battery alarm', see below. For example for me, true 85% was 4.33V, while true 100% is 4.44V. It will vary for your device. When protect battery is ON, 4.33V is now >= 100%.
I verified that when 'protect battery' is ON, the tablet stops charging at 100%; I use a current meter connected to the charge port, it drops to zero amps when 100% is reached, so the battery is really protected from higher charging levels. Note, this is the real 85% level, or 4.33V.
If you power off Android while connected to the charger using protect battery ON, the tablet will continue to charge to the real 100%, 4.44V, but a yellow warning icon appears, even if it shows 100%. I confirmed this, my current meter shows that charging continues, whether protect battery is OFF or ON, and with OFF, the yellow warning icon does not appear, and it won't stop charging until 4.44V is reached, this is shown on the current meter than current drops to zero amps. When you reboot Android and set 'battery protect on' after its been fully charged to 4.44V, the battery will be disconnected internally so it cannot charge, you will get a scary icon of a RED battery with a X on it, and the current meter also shows zero amps entering the tablet. It will reconnect once the voltage drops to < 4.33V or if you switch protect battery OFF. This is not documented anywhere but its reassuring, this means the hardware detects that the battery is potentially 'overcharged' , as with protect battery ON the full charge state has been artificially lowered, and now disconnects for protection of the battery.
To truly prolong the battery life, you could limit the depth of discharge, and there is no reminder to stop the battery from discharging to 0%. Software alarms can be set to any charge level of high charge or discharge needed to prolong battery life, the good range is between 85% charged, and 35%, discharge. I use Battery Alarm by Zoran Vujacic; its simple, does the job, has no ads even for the free version, but needs configuration in Samsung devices, see app for details. Where to set it? the smaller the difference between charge and discharge, the narrower the depth of discharge, which is good for prolonging battery life, but it will shorten your run time. For heavy users, use the extreme 85-35, for lightest users, use 80-50, and choose any setting in between that meets your needs. For example, I currently have a 3 old phones from 2010, using 80-50 the battery health app reports its 98% 'like new'. If you still need more power, lower the discharge level first, and increase the charge as little as possible.
