Does the MacBook have a backup (PRAM) battery?

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Level 2

491 points

Does the MacBook have a backup (PRAM) battery?

The MacBook replaces the iBook, which does not have a backup/PRAM battery. Does the MacBook have one? I've been unable to find any mention, pro or con, in the knowledge base or the MacBook manual. If anyone knows and can direct me to printed confirmation, I'd appreciate it.

PowerBook G4 17" 1.5GHz, Mac OS X (10.4.8), 1GB RAM, 80GB HD, DVD-RAM SuperDrive

Posted on Oct 10, 2006 6:04 AM

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Answer 1

Kappy

Level 10

362,007 points

Oct 10, 2006 7:12 AM in response to HandyMac

Yes. The MB and MBP both have a small lithium cell used to backup the PRAM. There's documentation somewhere but I can't remember exactly where. It may even be in the User Guide. It's a short statement that's part of instructions on replacing the main battery that says you can replace the battery when the computer is asleep or not connected to AC without data loss. The backup battery is able to maintain memory long enough to exchange batteries but only for a minute or so after which the power drain will be too much for the battery.

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Answer 2

HandyMac Author

Level 2

491 points

Oct 10, 2006 9:14 AM in response to Kappy

Well, thanks. I figured the MacBook probably has a backup battery since I can find no statement anywhere to the contrary. However, it's not mentioned in the User Guide, nor in the Battery Replacement Instructions (which insists that the computer must be shut down and allowed to cool before removing the battery). Nor in the MacBook Pro User Guide or Battery Replacement Instructions. So I'd still like to see it in print somewhere.

PowerBook G4 17" 1.5GHz Mac OS X (10.4.7) 1GB RAM, 80GB HD, DVD-RAM SuperDrive

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Answer 3

HandyMac Author

Level 2

491 points

Oct 10, 2006 9:37 AM in response to HandyMac

I'd also like to know if the backup battery is rechargeable, like those in (some? all?) PowerBooks, or simply wears out, like those in desktop Macs.

BTW, I found mention of the backup battery in the MBPro here, but it doesn't mention the MacBook. OTOH, Apple generally recommends against changing the battery in sleep.

PowerBook G4 17" 1.5GHz Mac OS X (10.4.7) 1GB RAM, 80GB HD, DVD-RAM SuperDrive

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Answer 4

HandyMac Author

Level 2

491 points

Jul 11, 2007 7:42 AM in response to HandyMac

In case anyone else would like to know, I finally found the answer to this question -- in the excellent repair manual PowerBook Medic: the MacBook does have a backup/PRAM battery.

MacBook Pro 17" 2.16GHz Mac OS X (10.4.10) 2GB RAM, 160GB HD, SuperDrive

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Answer 5

carl wolf

Level 6

14,631 points

Jul 11, 2007 6:35 PM in response to HandyMac

...and it is not user replaceable. For several generations, the Apple notebooks used a "super cap" as a backup power supply for the P{RAM.

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Answer 6

Jul 11, 2007 7:36 PM in response to carl wolf

The MacBook has a battery which keeps PRAM intact, but not a battery which keeps the RAM powered up while you switch the battery while sleeping without AC power.

This is unlike the PowerBook G4 - where you could change the battery while the computer was asleep, without losing the contents of RAM, which would require a reboot.

This is where the Intel Mac's 'hibernate mode' comes in. If the battery is removed, while the computer is asleep AND without AC power, the contents of RAM are lost. BUT, the restart after replacing the battery is much quicker than a reboot, because it reloads the RAM from the disk file it produced when entering sleep mode.

Quad G5, PB 15" 1.5Ghz,MacBook 2.0GhzCore2Duo Mac OS X (10.4.10) Logic Pro 7.2.3, Focusrite Saffire...

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