Recently I've been thinking about how to make use of different electronics that would be thrown away otherwise. The company that I work at current is friendly about letting me have garbage electronics although I know most larger companies are not. I was able to bring 6 laptop batteries home free of charge and test the batteries.
Inside the laptop batteries are a bunch of 18650 cells. They are cylindrical batteries slightly larger than AA batteries and are Lithium Ion chemistry. This means that you do have to be somewhat careful about the chargers you use to charge them.
In total from the 6 batteries I obtained 42 cells that when charged read a decent voltage. Of course this isn't really enough to test if the battery is good. I used a battery tester that simply charges the batteries and drains them at 500ma constant current and measures the total current (energy) consumed over time.
I found that of these 42 cells, only 4 of them were bad. I defined bad as below 70% of the rated current capacity. Often times battery packs fail because of only a few bad batteries. Sometimes battery controllers even log the number of cycles and simply stop functioning after a certain number of cycles has been reached.
At this point I had 38 18650's with reasonable capacity which roughly worked out to be 76,000mAh at 3.7V. It would be more, but since these batteries are old they obviously have slightly less battery life.
There are a surprising amount of devices that can be powered by 18650's but here are a few useful ones that I found.
- Power banks with 18650 slots
- LED controllers/amplifiers
- RC drones/helicopters
Inside common power banks is basically a Lithium battery combined with a power delivery and charging circuit. This circuit is what protects the internal battery from over charging, over draining, and controls the power output. That being said, power banks with better circuitry to handle higher currents are more expensive. On top of that, draining 18650s beyond 1A is not really suggested for most of them. However, I don't really care about over draining or damaging batteries since I already have too many at this point.
For 2 slot 18650 power banks (which can charge normal 5'' phones 1.5 times) you can get them for as little as $1-2 from Aliexpress. This is nice if you just need an emergency power bank somewhere to store in case your phone dies at a crappy time. I bought a higher rated power bank with 2 cells which I have tested up to 2.5A draw. It works super well for my phones and cost $6, really I just like the form factor.
Another interesting feature about larger power banks (such as a 4 cell) is that not only do they output more power with less current draw from individual batteries but they also tend to have more functionality. For example, I got a 2A rating power bank 4 cell bank for $6 as well. However it had dual USB slots with charging up to 3A total and a DC jack that could provide 9V, 12V and 15V. This is very useful for just quickly testing small electronics such as fans, voltage converters, monitor controllers etc.
With the 4 cell battery pack I was able to run my portable screen, with a chrome cast and a mini speaker (which has its own battery). It only lasted about 2 hours though before the batteries were dead. Although I don't really think this set up is particularly useful I do think its pretty cool that it can be done and this system can be made into a portable unit with this rather cheap addition.
Perhaps the most useful feature about this battery bank setup is that a 18650 charger can be used to charge each individual battery at 1A. Doing an easy calculation each battery can receive approximately 3.7W which is far beyond the charging speed of most battery banks (5V 1A input). Even compared to banks with a 5V 2A input capability, 14.8W average power input from chargers is still far faster. Of course, having charged batteries on deck to swap out is also extremely convenient.