How to build a portable battery

Tom Westrick

Well-known member
Apr 29, 2012
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I am looking for a new portable battery that would be powerful enough to charge both my phone and my laptop. Right now, my laptop is an Asus Chromebook C302 and it requires 45W to charge, but I'd like something that can charge in the 90-100W range in case I get larger laptops in the future. My full desired specs are:

2 USB-C ports that can output 100W of power. One/both of them would also be used to charge the portable battery itself. Support for USB-PD, if that's not already a given.
1 USB-A port, I'm not too concerned on the speeds for this since it will be used
27,000 mah battery, since that is the legal limit for taking a battery onto a plane
A plain black metal case
An LED battery life indicator.

I've seen instruction guides on building a portable battery, but they use older controllers with USB-A and micro-USB ports. I know this will require a longer answer than a forum post may be able to give, but anything you can do to point me in the right direction would be appreciated.

Jerry Hildenbrand

Space Cowboy
Staff member
Oct 11, 2009
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I'm going to try and discourage you from doing this. We're so used to low power low current batteries that we forget what kind of damage any chemical cell(s) can do once you're dealing with those kinds of power factors.

Having said that, point me at the instructions for one with legacy USB options that makes sense to you and I'll take a look. Basically, the storage side will be the same — cells are cells and all they do is store power. The regulators, input and output circuits and overcurrent protection would probably all need to be different.

And remember — building something like this could actually kill you. I(A) = P(W) / V(V) means you'll be dealing with (potentially) 20 amps. 200 milliamps can kill you if you really try, but 20 amps makes it easy.

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