# Do Desktop Computers have Batteries?



## Deep Blue (Sep 16, 2005)

This a technical question that stumped me. Someone told me other day that support staff constantly need to replace the batteries in their desktop computers (Emacs at a school).

I have never thought of desktop computers as having batteries - laptops only because they need a portable power supply.

Does anyone know if this is this true and, if so, what's the scoop on it?


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## CanadaRAM (Jul 24, 2005)

Yes, almost all desktop computers have a battery to keep the clock and the PRAM settings alive (CMOS settings, for a PC). These can be a lithium cell, alkaline cell or rechargeable lithium, depending on the model. THe most common Mac PRAM battery is a 1/2 AA 3.6V Lithium cell which you can get for $10-12 retail at a Mac dealer or a good electronic supply store. Some older Performa and LC machines used a 4.5V cubical alkaline battery.

Lifetime of a PRAM battery is 2 - 5 years, depending on the model, and how much time it spends being off/unplugged. The more the machine is off. the shorter the PRAM battery will last.

Typical symptoms of a failing PRAM battery is losing the date and time settings when the machine is turned off, network and startup disk settings randomly dropping or resetting, and finally; no video on startup or no startup chime and only a brief flash of the power light, when the battery doesn't even have enough juice to switch on the AC power.

Many laptops also have a battery on the motherboard that keeps the settings, although some only have a simple capacitor, meaning you have only a few seconds or very few minutes to swap batteries before it dumps the info.

Thanks
Trevor 
CanadaRAM.com


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## Deep Blue (Sep 16, 2005)

I am much obliged. Had no idea. That would explain why emails sent to me by this person had the date january 3rd 1970.

My yahoo account kept saying I had mail in my inbox but I couldn't find it. Since emails are organised by date, the new one's were popping in right at the back of my inbox, many screens away.

So that means when my Imac's $10 battery goes I'll have to spend $150 on a service repair. 

Will a machine run happily without a battery (knowing of course that the date and time functions are toast)? 

And how come, in 20+ years of running, using and owning computers I have never heard of this? Have never seen a desktop battery nor had to replace one. Am I the only one to be gobsmacked by this???


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## CanadaRAM (Jul 24, 2005)

Depending on which machine it is, the battery is dead easy to replace once you have the machine open.

First - open the machine. Check online for instructions on your specific machine.

Then - locate the battery - it will be in a rectangular black plastic 'cage' on the motherboard. Before doing anything else, make note of which way it is facing -- the end with the nipple on it is the + terminal. You want to put the new battery in the same way. 

The cage may have a top to it - it is easily removed by prying outwards gently on the 'legs' at the narrow ends.

Remove the battery

Now, this may be superstition or not, but if you slam the new battery straight in there, you may corrupt the PRAM. The general practise is to let the remaining charge in the circuit drain first. You can either leave the battery out for several hours, or you can use a screwdriver or paper clip to short across the terminals of the battery holder for 5 minutes.

Then put in the new battery (same direction !) and put the machine back together.

When you restart, you will have to re-make all the normal Control Panel / System Preference settings like Time and Date and Mouse Speed and network preferences. Only need to do this once, they should 'stick' now.


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## eMacMan (Nov 27, 2006)

Yep the big issue is that schools typically unplug over the breaks and the battery is being drained by the keyboard and mouse. Off time does not seem to have any impact. The battery in my eMac is still going after 4 years and it is off at least 18 hours a day.

To test the battery. Turn off the computer, unplug the internet connection and the computer. After 5 or 10 minutes plug the computer back in and reboot. If the date and time have held; the battery is still good. The reason for disconnecting from the network is that date & time is often automatically reset when you log in, so you will not know there is an issue until the kernel crash happens. 

With older iMacs, eMacs and Power Books replacing the battery takes less than a minute. The trick with a G3 iMac is to push the battery straight back while you lift the positive end up with your thumbnails.

Never heard the one about not just dropping in a new battery. I have replaced hundreds in that manner with no issues. Just be sure to properly discharge any static before reaching inside.


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## Deep Blue (Sep 16, 2005)

I am indebted to both of you for the information. 

I cracked open my Mac mini to replace the RAM but don't like the idea of fishing around inside when the battery needs replacing. Same goes for my Imac which I have never opened up.


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## CanadaRAM (Jul 24, 2005)

Deep Blue said:


> I am indebted to both of you for the information.
> 
> I cracked open my Mac mini to replace the RAM but don't like the idea of fishing around inside when the battery needs replacing. Same goes for my Imac which I have never opened up.


Battery's no harder than the RAM, really.


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## krs (Mar 18, 2005)

Does the battery actually need replacing if you don't unplug your Mac?
I have an eight year old G4, replaced the battery two years ago because it was staring right at me when I added another hard drive (and I thought with 6 years on the battery it's probably close to the end of its live). But after I put in the new one I bought, I tested the old one under load and it still provided the full voltage.

My Mac only gets unplugged when it gets moved which is very seldom.


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## Gerbill (Jul 1, 2003)

krs said:


> Does the battery actually need replacing if you don't unplug your Mac?
> I have an eight year old G4, replaced the battery two years ago because it was staring right at me when I added another hard drive (and I thought with 6 years on the battery it's probably close to the end of its live). But after I put in the new one I bought, I tested the old one under load and it still provided the full voltage.
> 
> My Mac only gets unplugged when it gets moved which is very seldom.


I've never seen one that lasted longer than 5 years, but I guess there's a first time for everything. My eMac ate its first one after about 3 years, and it's never unplugged. The eMac battery is really easy to replace - it resides behind the same little door in the bottom that's used to install RAM.


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