I had an old laptop battery that used to be in my Acer laptop but, after a few years of use, didn’t hold charge very long. I’ve since purchased an aftermarket replacement from Anker, which works a whole lot better. I knew the old one still had as many as 6 usable 18650 cells inside, so I decided to do a laptop battery pack teardown. It would be an interesting small project (I’d never seen the inside of a laptop battery myself before) and would yield a few rechargeable batteries (I like the 18650 size lithium ion battery and have started somewhat of a collection of devices that use them).
Disclaimer/Safety Warning: As you can imagine, opening a laptop battery (or any kind of battery, really) can be a dangerous activity. Beyond the very real risk of getting shocked, there may be sharp edges or pointy pieces. It’s possible to short-circuit the internal components, so there’s a risk of exploding lithium cells and/or starting a fire. For these reasons, it is not recommended you try this yourself.
Opening and Taking Apart the Laptop Battery
At first I figured the best way to get the battery open would be to twist the thing – enough to make an opening along the seams for a screwdriver, then crack it open.
After a little digging around online, I found out the battery isn’t completely sealed by the plastic, that the top is essentially just a label you can peel up. With the label off, I carefully removed the wires from their solders, trying not to let the ends touch anything metal. I also broke some of the plastic off from the case to make room for the cells to come out.
As I started to pull them apart, I noticed the batteries were connected to each other via small metal tabs. I snipped the tabs between the individual 18650 batteries in half using scissors, then needle nose pliers to remove the remaining pieces of metal tab still stuck to the ends. Looking closely at the photo at left, you can still sort of see the points where the tab connectors were attached to the positive end of the battery.
With all six 18650 batteries out of the plastic case and their tabs removed, I then checked their voltage. Although the nominal voltage of the 18650 is 3.7 V, in actuality the voltage might be slightly more or less. My multimeter was showing around 4V for each, which is good; anywhere from 3.3 to 4.2 is normal, with the voltage dropping as the charge is drained. It’s important to use and handle lithium batteries correctly, particularly when it comes to charging/discharging them.
Using 18650 Batteries in Series for Higher Voltage
Since the voltage of each battery is about 4V, it occurred to me that many electronics use a 12V power source – so three of them in series would do the trick. I had several 18650-size battery holders around, so I wired them together. Since they were connected to each other by soldered wire and metal tabs, these are “flat top” cells and don’t have a “nub” on the positive end like many common battery sizes (e.g. AA, C, D).
Since the battery holders only had a spring at the negative end, putting in the batteries was a little tricky. It took a few adjustments to get them all in a position where the contacts touched properly. Once setup, I then connected my battery pack to a 12V PC case fan by inserting the stripped ends of the leads into the positive and negative sockets of its Molex connector. As you can see below, it worked!
The fan spun well, moving an impressive amount of air. According to the multimeter, the current was .2 Amp, so the fan was using about 2.4 watts. I let it run for a few minutes, and then disconnected it (I’d be too concerned about drawing down the batteries too far to leave this running as-is, but it was fun trying it out.)
Next I thought about the other 12 Volt items I had handy, realizing that I’d need some way to make the connection. I didn’t have a spare 12-Volt DC plug handy, other than one designed for a cigarette lighter. Since I wanted to keep using this adapter in the car, I couldn’t just cut the plug off and strip the wires. I ended up temporarily attaching the positive and negative wires of the battery holders to their respective places on the plug.
On the positive end of the adapter, I screwed the threaded cap over the positive wire to make the connection. Then I wrapped the ground wire around one of the side tabs, taping over it with electrical tape to keep it in place (and prevent short circuiting).
I figured this would be a good way to go, particularly since the current runs through a fuse before it gets to the device being powered. A quick check with the multimeter showed 11.79 V – close enough!
Powering 12 Volt Devices with 18650 Batteries
I first plugged my homemade 18650 battery pack into an old WiFi router I had lying around. It powered up just like it was plugged into a wall outlet. If I made a proper container to hold the batteries and updated the router with new firmware, this could be useful as a sort of DIY portable WiFi extender to use in places that offer free wireless internet, but are a little bit too far away for a laptop to connect by itself (camping maybe?).
I have another WiFi router that has inputs for 3G/4G cellular internet USB-adapters, so it’d be a higher-powered (and free, since I have all of the parts) alternative to buying one of those portable hot spots. I’d want to figure out a way to keep the 18650 batteries from discharging too far, though (plus an easier way to re-charge than removing the batteries individually and putting them in an external charger).
I have yet to see an off-the-shelf 12 volt solution that supports 18650 cells in series and manages their charge, but it would be pretty neat. If anyone knows of something like this, ideally one with a weatherproof case, please let me know in the comments.