Battery Percentage at Login Doesn't Match Percentage after Logging in

[-=Hot|Ice=-]

So, I have noticed a slight issue on my 16" MBP that isn't new. The battery percentage that is displayed at the login screen is not the same as when I login. My login percentage says 96% but when I login, it shows 100%.

This issue goes away when I unencrypted my drive which is not something I'm willing to do.

This issue specifically has been around for awhile as I had it on both my 13" and my 15" MacBook Pros. I'm surprised nothing has been done about it yet.

Hoping this thread makes a big enough fuss to get Apple's attention and fix it.

 

[iMacDragon]

at login screen with encrypted it's not yet running actual OS, just a simple boot manager, and I'm guessing it's doing a simpler calculation that's probably closer to the 'true' percentage.

Like most systems nowadays, 100% is actually displayed for what is really 95-100%-ish, for whatever psychological reasons.

It's probably actually because this is the trickle charge area of battery, so they don't want it to seem like it takes forever for the last couple of % to charge.

 

[laz232]

at login screen with encrypted it's not yet running actual OS, just a simple boot manager, and I'm guessing it's doing a simpler calculation that's probably closer to the 'true' percentage.

Like most systems nowadays, 100% is actually displayed for what is really 95-100%-ish, for whatever psychological reasons.

It's probably actually because this is the trickle charge area of battery, so they don't want it to seem like it takes forever for the last couple of % to charge.

I'm quite sure that the reason for this is the following:
A battery is a collection of individual "cells"

State of Charge (SoC) is mainly determined by cell open circuit cell voltage.

LiIon batteries can be charged to 4.2V per cell.

Doing so frequently causes a reduced cycle life - especially when they are warm, therefore under most circumstances cells are charged somewhat less (to ca 4.15V).

Most users expect to see 100% charge after being plugged in, and Apple would constantly get support calls asking why battery is not charging to 100% - therefore upon login the system will lie to the user.

Install Coconut battery and you can see the discrepancy whilst logged in as well.

L (senior member IEEE)

 

[haginile]

I'm quite sure that the reason for this is the following:
A battery is a collection of individual "cells"

State of Charge (SoC) is mainly determined by cell open circuit cell voltage.

LiIon batteries can be charged to 4.2V per cell.

Doing so frequently causes a reduced cycle life - especially when they are warm, therefore under most circumstances cells are charged somewhat less (to ca 4.15V).

Most users expect to see 100% charge after being plugged in, and Apple would constantly get support calls asking why battery is not charging to 100% - therefore upon login the system will lie to the user.

Install Coconut battery and you can see the discrepancy whilst logged in as well.

L (senior member IEEE)

This actually makes a lot of sense... I've been observing a ~5% discrepancy between what the system reports and what Coconut Battery reports (after some discharge) and I was silly enough to file a bug report....

 

[Weaselboy]

Most users expect to see 100% charge after being plugged in, and Apple would constantly get support calls asking why battery is not charging to 100% - therefore upon login the system will lie to the user.

Exactly... Apple fudges the numbers in the GUI. If you install Coconut Battery or look in System Report and do the math yourself you will see the true number.