DIY laptop battery pack (textbook size)

it took me a long time to find a suitable forum to ask this.

I have a thread at Cnet, a tech site.

I'd really like to have the power I need to last through the school day, and I'm sure other students feel similarly. 

I thought about solar, but it's too low of a yield. Nimh and Ni-cad have shorter lifespans than Li-ion.

What's necessary in this setup would be:
small enough to fit in a backpack
thin enough to leave room for my books if need be
must be able to fully recharge a laptop at least once while in use.
AC current preferred, DC if necessary, I can get an inverter.

I have a soldering gun in my electrical kit and would love to show off to my friends next school year.

edit: I forgot to include that this is to use with a laptop

update: I've decided that I can use a briefcase if I get a slightly larger backpack next year. I found some batteries, and I'm trying to figure out the voltage and amp-hours for the PCB and charger


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So, the white boy with a big mouth side of me is going to say "prove your intelligence, and competence to your friends regarding a subject you have absolutely no idea about".

But then again we all started somewhere... Take an old laptop battery apart. Check it out, the type of battery, the general layout of it.. Take pictures if necessary.. Do a little research and find the equivalent readily available on the internet batteries you want to use, for every 1 battery in your current battery pack you'll need at least two. wire the pair of new batteries just like your 1 is now but paired.. So you'll have two batteries soldered together + + and - -. Attach the positive side to the next pair of batteries, and the - too. Just like your normal battery case was. The result with be the same voltage you've got in your normal battery, only twice the battery life. Repeat those steps as necessary, it'll end up being less than an inch thick, and whatever dimensions you want it to be..
leaf26 (author)  Jackscantflash4 years ago
If I want to be honest and say that part of me just wants to show off, why not?
Did you come up with a plan? how'd it work out? The suspense is killing me!
leaf26 (author)  Jackscantflash4 years ago
yes, I have, but it was postponed until thanksgiving break. I had summer reading, a college essay, and a little summer review work for two AP classes this year. I procrastinated it too long.

The plan is to go the li-ion route and wrap each cell in vented printer paper so I can direct the heat distribution. I'm increasing the budget by 50 to create a more controlled device.

To regulate the voltage and step down that 16.8v, I added a powerful voltage regulator to the build:

To help dissipate heat, I'm considering modding the case to add a computer fan (80mm, "silent", probaby under 4.5w@12v), and if I do so, I'll need to add a small switch.

Will add to comment later, gtg
leaf26 (author)  leaf264 years ago
Looked up the 80mm consumption:

It's under 2w, so that should be nice. that means for a 4s4p battery pack rated 142w, with fan on at all times, it would go for about 70 hours not including power draw of other components.

if I'm going to use a switch for the fan, it should be automated and more efficient than the fan. here's a thermal controller, but it requires 12v and 5v:
I strongly recommend not trying to take it through an airport, or leaving it unattended in any public place. Taking it to school, where they know you, you'll just have to explain what it is. No wires showing, no crazy bomb like contraption unless you x ray it.. Just a clean thin plastic case you could even strap it under your current laptop if you're using it on a desk.
What laptop brand and model do you currently have? Many manufactures offer an extended life battery pack that will attach to the bottom or back of the laptop to double your battery life. Or you can find a battery upgrade that fits in the current battery slot.

Obviously your not able to plug your laptop in during class so you may need to just buy several batteries to keep in you bag and charges for them so you can charge them at night.
leaf26 (author)  mpilchfamily4 years ago
External battery pack, AC output using inverter
If your asking if it would be good to have a large battery powering an inverter so you can plug your laptop into it, its a very bad way of doing it. An inverter will drain even a car battery within a couple of hours. There is also a large amount of energy loss converting the DC to AC. You would be better off adapting the battery to supply the required voltage directly to the laptop's power connector. But that isn't a safe idea.
leaf26 (author)  mpilchfamily4 years ago
how about a more common DC car port?
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