Need another battery for your Mac? Try this

Ok, so here’s the problem. My laptop lasts for 2 hours, maybe three at the most, if I’m lucky. Sometimes you’re on a long flight and you want to get more work done. You need another battery (or a seat in business class!)

With IBM/Lenovo laptops, it used to be easy to buy a modular hot-swappable additional battery for $70. It turns out that’s a lot harder for the Mac. I found this Hyper Juice Battery for $300, but that didn’t seem like a terribly good deal to me.

How hard can it be to make one yourself?

Here are the ingredients :

12v mac car-charger

The power brick that comes with your mac converts AC mains power into 14.5v DC power. Since you’ll be boosting your laptop with a regular battery, you’ll want to pick up a 12v Mac power adapter for your car.

Mac Car Adapters on Amazon – These all seem a bit shoddy, but they seem to do the job.

Cost : $30

12v Lithium Battery

You’ve got a 12v adapter. Now you just need a 12v battery. You’ll want to pay attention to a couple things… capacity, technology, and voltage.

1. Battery capacity. – The battery in my macbook air is rated at 4800mAh. So if you get a battery that is about that size, you will double the time you can work on your computer.

2. Battery technology. – Lithium ion batteries seem to be able to offer the best price-weight-capacity ratios. But there are many different types of lithium batteries, and some are quite unstable. Check out this video!

I did a little research, and found that Lithium-Iron-Phosphate (LiFePO4) are probably some of the safer lithium batteries. Small lithium batteries are allowed on airplanes under TSA regulations.

3. Voltage. – You’ll want to assemble your battery so that it outputs 12v or slightly more.

I ordered this 12.8v 4500mAh LiFePO4 battery from BatterySpace.com

Cost : $60

Connections

Now you just need to connect it all up. I bought a cigarette lighter socket from Radio shack and ordered a bunch of XT60 connectors online, and wired it all up.

Cost : $15

My jury-rigged battery system now looks like this :

photo 1

The battery will fully recharge my MacBook Air, while runnning, before it runs out of juice.

Charging technology

Wait! – The game’s not quite over, because you need to recharge the battery now. LiFePO4 batteries are sensitive to overcharging, and are best charged by a specialized charger. I ordered a Turnigy Accucel 6 charger that seems to be quite popular in the radio-control hobby market.

Cost $30

Now the charger also needs a DC power supply, so I had to repurpose an old laptop charger to do the work. This all added a bunch of extra weight to my baggage!

photo 2

I’m looking into ways to use my regular mac power supply for powering the charger instead of having to carry an additional block! It’s not simple though, as the mac power supply has circuitry built in to engage it only when conneted to a computer, but stay tuned.

So the end result is $135 for a very ungainly DIY battery pack. They let me take it through the last 6 airports I’ve been in (SFO, HKG, MNL, KLO, GUM, HNL) even though it looks just like a small bomb! – I’ve found this to be a great talking point with fellow passengers!

And, when you’re not flying, you can use the battery to power LED Christmas lights on your bike!

bike_light

3 Responses to Need another battery for your Mac? Try this

  1. Aimee Michaels says:

    Hey, why do you need the 12V to 14.5V converter? Why not just use a 14.5V battery?

  2. Anton says:

    I have had success and fun taking dead battery packs from old laptops out if the recycle bin at my local hardware store and other places. There is usually one cell out of the string that is bad and the rest are serviceable.
    If you go to Hobby King you can get s lithium charger that will run off 120-220vac.
    The only remaining concern is that over discharging lithium cells is bad too, but if you’re careful it shouldn’t be a problem.
    Hobby King sells a battery monitor for $12 that plugs into the charge equalizing plug that you use to charge it that will alarm when the battery is low.
    I have used this setup for bike lights racing motorcycle batteries and for reviving battery drills!

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