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I have about 20 batteries I want to test. I'm trying to find out if they will read "replace" or "service" in the OS. Usually, I'll stick the battery in long enough to collect a cycle count and condition. However, it seems that a lot of the batteries shortly after show "service" or "replace". Maybe, once booted for the first time in a while, the computer assigns a new battery condition to the battery. If so, I should install the battery turn on and then restart a second time before collecting the battery info. I'm curious if maybe it takes macOS a while to assess the condition of a battery and, if so, how long it takes. What do you recommend for quickly assessing the condition of a battery? Thanks.

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  • what equipment do you have to test battery outside of a Mac ?
    – Ruskes
    Dec 13, 2018 at 15:56
  • I don't. I usually stick the battery in a Mac, boot from an external USB HDD with an OS preloaded and collect the info. The process usually takes a couple minutes but I'm finding that it isn't accurate. Several batteries shortly later show "service" "replace" even though they displayed "normal" in the OS when I collected the info. I just remembered coconut battery. I might try that too.
    – www139
    Dec 13, 2018 at 16:12
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    More than likely, you'll need a specialized battery tester tool that can not only read the smart chip on the battery, but also test the battery itself under load. What you're getting from the laptop (MacBook) is neither highly accurate or efficient.
    – Allan
    Dec 13, 2018 at 16:48
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    Buying a battery tester that costs $500 that is equal to about 10 new batteries might not be economical.
    – Ruskes
    Dec 13, 2018 at 18:08

1 Answer 1

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Battery SOC is always time dependent.

Determining the state of charge (SOC) in lithium-ion batteries is essential yet challenging due to the great variability in capacity not only across different cells, but also in the same cell. As a Li-ion cell ages, it loses its ability to store charge. Consequently, even if fully charged, an older cell would deliver usable voltage for a shorter period of time than a newer cell.

While in the first moments it might look OK, soon after it shows the true State of Charge.

That is because it measures Voltage and Current variations over time to determine the SOC.

I recommend at least 10 minutes of testing of allowing the Mac to collect the information.

The State of Cycle count is only a indicator for us humans, but not accurate to determine the true state.

Probably the best indicator is the

Full Charge Capacity (mAh): 6705

Found in About this Mac > System Report > Power

It basically says how much charge the battery can hold.

It is not a linear scale thus when it reaches half a way of new battery (4000) Mac will say service the Battery.

New battery has values of >8000.

What is the most accurate method of testing batteries for A1278 MacBook Pro?

it is TIME allowing it to collect the information time related.

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  • Thanks for the excellent answer. This is exactly what I suspected. Thank you.
    – www139
    Dec 14, 2018 at 15:13

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