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My portable charger is probably the most useful piece of technology I carry with me, other than my phone. I am terrible about remembering to charge my phone until I’m stuck on a delayed subway at 7PM on my commute home, desperately trying to squeeze out the last few seconds of battery life.

So, I’m generally of the opinion that there’s no such thing as having too many backup chargers. (I tend to carry three with me, which I will acknowledge may possibly be overkill.) But buying a battery pack from Amazon or Best Buy is easy.

I wanted to try to make my own — and I managed it without even electrocuting myself once. The DIY battery pack here is essentially a USB phone charger that runs off 9V batteries, all dressed up in a fancy aluminum…

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