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I have old MacBook Pro that has a dead battery. It is not charging, and displays always 0% battery charge.

OS X is downgrading performance when battery level is close to something about 5% or 10%.

Is that possible to turn off this feature, to be able to use its 100% performance without exchanging battery to new?

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    If you are using the power adaptor, then there shouldn't be any performance reduction. But really, you need to get the battery replaced. – benwiggy Aug 9 '20 at 15:35
  • It is immediately turn off without power adaptor. So yes, I am using it and yes there is performance reduction for sure. – gkucmierz Aug 9 '20 at 15:56
  • Welcome to Ask Different. As commented before, I'd expect a failed battery to not affect or reduce performance in any way. What makes you think this is the case and it is related to the battery? Couldn't it be some other issue like a OS upgrade or installed software? – jaume Aug 9 '20 at 17:56
  • Welcome, because it happend exactly when battery died. – gkucmierz Aug 9 '20 at 19:21
  • What exact model is it? – lhf Sep 1 '20 at 18:32
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On the older MacBook Pro models, it's not a software function that reduces power. It's actually a hardware requirement, managed by the SMC to utilize both mains and battery to get full performance. With a dead or missing battery it would actually "downclock" the CPU.

MacBooks Run Slow Without Battery*

If the battery is removed from a MacBook or MacBook Pro, the computer will automatically reduce the processor speed. This prevents the computer from shutting down if it demands more power than the A/C adapter alone can provide.

With newer MacBooks and the release of Catalina's Battery Heath Management feature, you can control (very limited, albeit) whether or not performance is affected.

However, in your case, you would actually see better performance if you removed or just disconnected your battery because the charging circuitry is using current that could otherwise be used for processing to try and charge a battery that will not hold a charge - in effect, you have a power "drain" on your computer which is compounding the issue.

You need to replace your battery with a quality unit


* Tom's Hardware, Marcus Yam, Marcus and Ngai, Amos; December 01, 2008. https://www.tomshardware.com/news/apple-macbook-pro-battery-benchmarks,6643.html

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    So how can I fool it to think that battery have 100% charge? I remember there was some option in some plist files or something like this, but I cant remember where to find it. – gkucmierz Aug 9 '20 at 16:13
  • You can't trick it. Battery charge isn't stored in a plist. 1) because charging is not a function of the OS - you can charge when the computer is off, right? 2) the battery information is continually calculated based off of measurements taken from the battery which is managed by the SMC. Batteries for older MacBook Pro computers are actually not expensive at all - around $50-75USD for a quality unit. – Allan Aug 9 '20 at 16:20

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