DIY Li-Ion Jumper Box (and battery bank)

I’ve got oodles of Li-Ion batteries around for my flashlights, and I want to put them into use in something productive.

Has anyone seen an empty battery box that can run 4x 18650 in series to jump a car battery, but also has a USB plug for charging devices?

Or, at the very least, seen a battery box that could be wired up with heavier gauge wires with batteries in series?

I think you would need a LOT more than 4S to deliver the amps required for car starting. The jump starter I have probably has at least 20 cells (4s5p) in it based on size alone, if not more.

4s might get you over the top if the battery is a little low. The motorcycle l-ion batteries look like they’re at least double that size.

Since you need hundreds of Amps - LiPo is the way to go.
Even the best 18650s don’t come over 30A or so, so you would need a lot of them in parallel.

People have posted here that they have used rc lipo packs

Technically, this is what you’re asking for, but I agree with the previous posters that it likely won’t have the current to jump-start a car.

I have a couple, and they work pretty well. Just don’t put any battery in wrong, or the springs are toast. Well, I’ve heard that.

That pack is a 2s2p (8.4v) so is unsuitable both from a voltage and an amperage ability.

You are correct.

Hey thanks for shutting me down, guys!

Gotta learn and embarrass myself somehow!

Well, unless you have a battery box that can hold 21700s to use Samsung 30Ts, you are out of luck.

Along with some very low resistance contacts, such a build would be quite interesting.

How many 18650s would you like to use in your design?

Something like a 4S4P arrangement would work pretty well for cranking with sufficiently powerful cells.

On the other hand…I’ve seen someone trickle charge a car battery with a crap load of AA alkalines.

If you’re patient this might still work :wink:

I had one of those glove-box battery jumpers. It died on me, so I took it apart. It was just a 3s LiPo and a circuit board that handled charging, a USB port, and a multi-color LED. I was surprised to see that it actually charged the battery through the balance port. I bought it for $110 at the time (maybe 4 years ago at the NY Auto Show) but I could probably build a better one for about $50 in parts and an afternoon.