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MetroMPG 12-20-2009 02:06 PM

What would you do with a small collection of 18650 lithium cells?
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This is my little pile of laptop batteries, made up of "18650" lithium cells - the same cell format Tesla uses in its roadster.

Even though I only have to collect 6798 more cells to make my own Roadster battery pack, I'm thinking that might not be a realistic goal. ;)

The top battery was brand new last summer - right after I got it, the internal battery charger in the laptop died, so I ended up getting a new laptop.

The other two are old batteries of unknown condition - probably not too healthy.

I hacked them apart just to have a look-see. Never been inside a laptop battery before, or played with lithium.

Anyone have any creative ideas? I don't want to just recycle them if there's some other interesting life they could lead. What would you do with them?

thatguitarguy 12-20-2009 02:20 PM

I too wonder about this. "Dead" laptop batteries are pretty easy to come by. I wouldn't mind hacking them apart to find if any of the cells are good and could be used on other projects.

My understanding is that the challenge is in charging lithium cells without damaging them, or creating the potential for fire. I don't know anything about devising chargers that would be safe and effective, or I would go for it.

RobertSmalls 12-20-2009 02:27 PM

You should use them somewhere that needs a lightweight battery. Probably on something portable, or on a bicycle.

14.8V is a nice voltage. You could probably run 12V auto accessories on it, or a bicycle illumination system. Maybe put a car stereo in your canoe?

How big is "18650" compared to AA?

MetroMPG 12-20-2009 05:54 PM

I just realized one thing I could do: I can take the "good" cells (top battery) and swap them into the bottom battery - it's the original battery from my newer laptop, just replaced this summer. I should have done that in the first place, instead of buying a new $60 battery. Wasn't thinking!

That would give me a 2nd battery. I wonder if I could parallel them somehow that wouldn't freak out the computer/battery circuit...


Guitar: my limited understanding is you can charge them "safely" at low current until they approach full voltage. That's when the potential for trouble starts. So, if you don't have a smart charger, and are willing to give up some capacity (by stopping the charge a little early), you can use a dumb charging method.


Robert: 14.8v.... yes! Reminded me of another potential idea I had: a "boost" pack to support alternator-less driving. Something relatively light & portable that could be plugged into the cigarette lighter.

If I could track down some more decent cells, that might be a project.

I keep thinking of this (and probably saying it) but I may have a couple of sources for used cells. I know a guy who runs a computer store, and another who runs a Black & Decker warranty repair depot. I wonder if he's handling cordless lithium stuff in his work ...

MetroMPG 12-20-2009 06:02 PM


Originally Posted by RobertSmalls (Post 149007)
Maybe put a car stereo in your canoe?



How big is "18650" compared to AA?

Diameter 18mm + or - 0.2 mm Length 66mm + or - 0.2mm. If you are talking an old AA flashlight it will not work. 18650 is to large. AA are 14.2mm in diameter and 50mm in length.
According to 18650 - what are the dimensions? [Archive] - Bike Forums

thatguitarguy 12-20-2009 07:04 PM

I'll have to do some more research on this subject because I keep getting more DC devices, and lithium seems to be the current best storage technology. If I could build a device to test individual cells and learn more about BMS, I could upgrade my equipment that's still using NiMh.

MetroMPG 12-20-2009 07:19 PM

That would be the key: making some kind of test rig so you could rate/group your cells by capacity.

It's the same issue anyone runs up against if they're using used batteries in a conversion, like the ForkenSwift. Used is fine, as long as your weakest battery meets your range target. But if you're getting the dregs in terms of old batteries, it's nice to be able to test before you go to the trouble of putting it in the car.

FYI, here's one DIY way to capacity test old 12v batteries that conceptually could be applied to lithium cells: Easy Test of Battery Amp-Hours Capacity

RobertSmalls 12-20-2009 09:57 PM
That's hilarious. At the top, amps. At the right, hours.

I have a slightly more expensive apparatus that measures Ah, among other things: MRC - BATTERY CHARGERS Series - SUPER BRAIN 989, Item: RB989, RC PRODUCTS/BATTERY CHARGERS

Christ 12-20-2009 10:02 PM

I'd put 'em in my remotes and anything that requires batteries. :)

You can get sabot to load them into any other cell size, the laptop cells are almost always "AA" cells.

Other than that, I'd just start building smaller packs for anything you might need a battery for.

NiHaoMike 12-20-2009 10:13 PM

I once put together a simple circuit to check the capacity of rechargeable AA batteries. I had a single transistor and two resistors as a voltage detector along with a switchable current sink (two transistors and two resistors) and a relay to connect a charger. I had the circuit connected to the RS-232 port on my PC (two output lines controlling the relay and current sink, one input line checking the voltage detector). I wrote a simple Java program to first connect the charger for a few hours, then disconnect the charger and connect the current sink while polling the voltage detector every few seconds. It then calculates the capacity once the discharge is complete.

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