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riddle me this: why is a laptop slow when power adapter is connected but battery is low?
Posted by: space-time
Date: October 10, 2018 07:38PM
so I am having an extremely bad luck that 2 laptops (2011) failed days apart. Apparently kids reported the 13" being slow and not charging 1-2 days ago and today the 15" succumbed to the same failure scenario as I was using it in the morning.

So the 13" felt very slow today with 1-2% battery and not charging, and 60 or 85W power adapters connected. As the 13" machine ships with 60W which is enough to run the machine and charge the battery, I would think it should run at full speed. even more so with 85W adapter. yet, when battery was low, computer was running very very slow.

eventually like magic battery started to charge and now it is at 70%. I started the computer and runs at full speed again.

meanwhile, I was using the 15" machine on and off the charged and eventually the battery ran low and refuses to charge, and now that machine has the same symptom: it runs very slow.

so both computers run extremely slow when battery is low and not charging.

Why?

EDIT: and why is spotlight reindexing this drive all of a sudden?



Edited 1 time(s). Last edit at 10/10/2018 07:38PM by space-time.
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Re: riddle me this: why is a laptop slow when power adapter is connected but battery is low?
Posted by: GGD
Date: October 10, 2018 07:46PM
Probably for the same reason that the older laptops with removable batteries ran slow with the battery removed. Apple lowered the clock in that situation because it was possible that the computer could draw more power than the charger could supply, and with no battery to supply the extra power the computer would shutdown.

This is the same reason why Apple lowered the clock rate on some iPhones when their battery was getting too weak, but people thought that was some sort of conspiracy.

Don't know about spotlight, maybe the date was getting reset due to the power issues and confusing spotlight about what was indexed.
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Re: riddle me this: why is a laptop slow when power adapter is connected but battery is low?
Posted by: space-time
Date: October 10, 2018 07:47PM
I mean really really slow. Like booting into safe mode and no drivers were loaded. that slow.
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Re: riddle me this: why is a laptop slow when power adapter is connected but battery is low?
Posted by: Lew Zealand
Date: October 11, 2018 12:06PM
This is by design.

Like GGD said, this has been employed from time to time as the total power draw from the laptop running at max CPU and GPU can exceed the power that the adapter can provide, and then need to depend on the battery to make up the difference.

The 2006-2010 MacBooks did this because they could easily outdraw the 65W that their power adapters could provide and thus if you removed the battery, it ran at only half speed.

The 2011 15" MacBook Pros also do this as the well-used one I received recently had a dead battery and would only run at 800MHz, not the 2.3GHz it was rated for, much less the 3.2 Turbo it's capable of. I replaced the battery with one from our fine forum sponsors and now it runs like a champ, full speed.

Based on Space's post, Apple also does this when the battery charge is below a certain threshold, I believe 5%. I saw this in action when I was testing a 2016 13" MBPro, which went into limp-home mode below 5% battery.

You can confirm all this using the Intel Power Gadget, which reports the CPU and GPU speeds, CPU (and iGPU) power draw, as well as CPU package Temp and utilization. It is the first piece of software I install on any Mac I use:

[software.intel.com]
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Re: riddle me this: why is a laptop slow when power adapter is connected but battery is low?
Posted by: space-time
Date: October 11, 2018 01:25PM
thanks, that makes sense now. I installed the IntelĀ® Power Gadget and it installs fine, the web page says it requires Mac OS X 10.6 or later but when I try to run it, it tells me I need 10.10 or later.
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Re: riddle me this: why is a laptop slow when power adapter is connected but battery is low?
Posted by: NewtonMP2100
Date: October 12, 2018 03:21PM
....perhaps you secretly.......want a man with a slow hand........???



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