Build your own battery?

Discussion in 'Mac Pro' started by mrgreen4242, Mar 8, 2006.

  1. mrgreen4242 macrumors 601


    Feb 10, 2004
    So anyone here ever make their own battery pack for a laptop? I've seen a couple sites where people have done this, for both Macs and PCs, and was curious.

    I'm a pretty fair hand with a soldering iron and a dremel, so I might give it a go sometime, if I can find a cheap dead donor battery (something that is recongnized by the computer but only holds a minute or two of charge).

    It looks like a lot of these packs are made up of battery cells that are fairly common sizes, and it's just a matter of getting the right number of the correct sized batteries then soldering them in place.

    So any success, or horror, stories of someone rejuvinating an old laptop with a new hand built battery?
  2. R.Youden macrumors 68020


    Apr 1, 2005
    I did see someone power a laptop from a potato (OK they had a hell of a lot of potatoes!) in the same way as those small clocks did that you used to be able to buy. Not sure about building your own batter though. Maybe you could do something with an old car battery...
  3. mmmcheese macrumors 6502a


    Feb 17, 2006
    Open the lithium ion batteries under water if you're feeling adventurous.
  4. R.Youden macrumors 68020


    Apr 1, 2005
    I suppose if you think about it, it would not be that hard to do.

    All you need to know is the voltage input to the laptop (3.3V maybe, I cant remeber off the top of my head). Then of you can find out the mAh of a battery and then connect enough in parallel to provide the correct amount of power...

    Easy really!
  5. mrgreen4242 thread starter macrumors 601


    Feb 10, 2004
    It doesn't seem hard at all. You just have to pull out the old cells, get new ones of an appropriate size and voltage, and replace them in the same configuration at the ones you pulled out.

    Most laptops use 9.6-14.4 battery packs, btw. I am sure someone will leap in and say "WELL the blah-blah-blah uses a 6 volt pack and the blahblahblah2 uses a 16v!!!", but for the most part they fall into that range.

    I've also considered that with the older G3 PowerBooks you could make a battery pack with very cheap AA/AAA NiMHs that you could use in the secondary bay AS LONG AS YOU DIDN'T PLUG IT IN WHILE THAT PACK WAS IN THE COMPUTER. You'd have to charge it seperately. Probably safer to build an external pack that outputs the correct DC voltage into the main power port.
  6. Anonymous Freak macrumors 603

    Anonymous Freak

    Dec 12, 2002
    First, find the BATTERY power input of the laptop, measured in Volts. For most Apple's, it has been 12V, with a few exceptions.

    Second, connect batteries in SERIES until you reach that voltage. (Most NiMH batteries are 1.2V, so you'd need 10.) Call this grouping of batteries a 'pack'.

    If you want more CAPACITY, then create another series of the same voltage, and connect the two packs together in parallel.

    The milliAmp-hour rating is the amount of total energy the battery contains. No matter how you connect the batteries together, you add their mAh ratings together. So if your laptop drains 1000 mA of power when on, and you have a 4000 mAh battery, then you will get 4 hours of life out of it.

    You *DO* have to make sure that your battery is capable of outputting the power your laptop drains, but most batteries, when put in series with the number of others you'll need to reach the right Voltage, are capable of just about any rate of power drain that you'll throw at it.

    Series (if each battery is 1.2V, then this will produce 2.4V):
    - OOO - OOO -

    Parallel (if each battery is 1.2V, then this will produce 1.2V):
    -< >-

    In both examples, if the batteries are 2000mAh batteries, you'll have a total of 4000mAh of energy available. Connecting in series does increase the mA draw available, but connecting in parallel increases it moreso. So, for example, if you had batteries capable of supporting 500mA draw, connecting 10 in series MIGHT get that up to 1500mA (at 12V,) but connecting in parallel might get it to 5000mA draw (at 1.2V.)

    For reference, my MacBook Pro's battery, according to System Profiler, is running at a voltage of 11.5V right now (it was 12V earlier, the voltage drops a little as it drains,) has a max capacity of 5579 mAh, and is drawing 1576 mA right now. Earlier testing had minimum power draw at 1149 mA, max power draw at 3427 mA.

    I am not an Electrical Engineer, but I did take some EE classes in college. So all of this rests on my rusty memory. Feel free to correct me if you actually are an EE.
  7. mrgreen4242 thread starter macrumors 601


    Feb 10, 2004
    Hehe, I am/was an Army radio tech, that sounds about like what I remember from training. :p

    The older PowerBooks (which I suspect are much better cadidates for something like this) seem to have a range of 10.8v to 14.4v batteries, depending on the model. The input from the charger is 24v, if I recall.

    Building a new battery pack to replace an old one (using Li-Ion cells) will run anywhere from $50-100 depending on the exact models (it looks like Wallstreet owners might be out of luck, they used a more difficult to find cell size and used 12 of them :eek: ). Building an external 24v 5A pack out of NiMH C cells would run about $60, and could have a replaceable end on it so you could use it for any 24v system. Oh, it's weigh ~4 pounds. :p

    You'd have to buy/build a charger for it though, pulling 20 cells out of the pack and recharging them in a little wall unit or something would suck. Not sure how long 5A would power a Wallstreet or something like that. Couple hours at least.

Share This Page