Technically minded Weblog

This isn’t my normal topic, but it’s something I’ve been doing for quite a while.

1. The story

I’ve probably mentioned before that I do computer servicing as a hobby. Nowadays, I have very few customers (my guess is due to a small repair shop opening locally some time ago – people for some reason seem to trust companies more than individuals, no matter how much experience or what reputation you have in your field of work).

But in the past, I used to get a lot of systems for servicing. Among those systems were many laptops.

Unfortunately, while desktop towers can usually always be serviced in one way or another, some laptops that people brought me were beyond economical repair. Problems such as fried GPUs, bad tantalum capacitors, etc. were common back in the day. My offer in these cases usually boiled down to just salvaging data from computer’s storage and sending the computer to e-waste. Often, after salvaging data, owners would just leave those dead computers to me for spare parts.

And many of those computers still had their batteries installed.

2. Cell salvaging

Older laptop batteries were usually made from a bunch of cylindrical 18650 Lithium-ion cells connected in various series-pair configurations (nowadays, they mostly use Li-Po cells instead, altough 18650s are still common). Usual configurations are 4×2, 3×2 and 2×2, depending on laptop’s power requirements. Cell capacities also varied, older systems had 2000-2200mah cell, while newer ones had bigger 2800mah cells. Despite the battery itself usually being disabled by it’s electronics, those cells usually still had some voltage and would happily take a charge. Surprisingly, many even charged to their full rated capacity (there’s a catch – read further).

Sanyo/Panasonic cells were some of the best performers (I have several working cells from early 2000s !), while Samsung cells often had degraded capacity. LG were the worst performers, usually with really high internal resistances and somewhat degraded capacity. But even good cells from these laptop batteries did show signs of age. They often had increased internal resistance and degraded capacity at higher loads. But nevertheless, there are still uses for them as not all devices need high currents to operate.

3. My uses for salvaged cells

My most common use for these cells is building power banks. But not your usual power banks for charging gadgets but those which can produce higher voltages. Voltages like 9V, 12V, 12V, etc. These can be used to power various low-power electronic devices which are normally powered by wall-wart style power supplies (e.g. routers, switches, 3.5″ external drive boxes, amplified audio speakers, etc). These banks are useful for using those normally mains-powered devices on the go or powering them during power outages (which aren’t that uncommon in my part of the world during thunderstorms in summer months).

To build those power banks, I use DIY boxes from AliExpress branded “Aili”. These used to be dirt cheap (few EUR a piece) but prices seem to have risen nowadays. 6 and 4-cell versions are available. These boxes do have USB outputs which can work for charging your phone, but they are usually only 2 amps and are inefficient due to those cheap boxes relying on linear instead of switch-mode DC-DC step-down converters for their 5V USB outputs. Unlike your run-of-the-mill power bank, those boxes are optimized for higher voltage applications, not gadget charging.

6-cell version can output voltages up to 20V (5V, 9V, 12V, 15V, 19V and 20V) at 3A, while 4-cell box does up to 15V at 1.5A (lower voltages at up to 2A). One downside of the 6-cell version is that it requires at least a 15V power supply to charge cells with it’s built-in charger. 4-cell unit uses micro USB instead.

Those “Aili” boxes use standard barrel jacks for higher voltage outputs, with male-male power cables included with the box.

Nowadays, with the arrival of USB-C, there are DIY power bank boxes available on AliExpress which do support USB-C PD. Unfortunately, most of these boxes seem to top-out at 22.5W (even ones with 16 or 24 cells), my guess is because the great majority of them use a all-parallel configuration instead of series pairs (like the “Aili” boxes). Also, they rarely have anything besides 5V output.

I did find one vendor which sells custom-designed powerbank boxes with USB-C PD 60W or even 100W output capability. Interestingly, they do come in clear acrylic cases and can even be bought partially assembled as kits. They aren’t cheap but I shall order one anyway to try out as they seem to be well built.

4. There’s more…

Although they uncommon, factory-made powerbanks based on 18650 cells do exist. I just found that out after opening my beefy old 65W 20800 mAh USB-C powerbank (which had it’s magic smoke escape while charging) to salvage it’s lithium cells. Instead of the usual stack of Li-Po cells, I found a pack of 8x 2600 mAh 18650 cells in a 4×2 series pairs configuration. Interestingly, the battery pack has it’s own separate PCB, similar to those found in laptop batteries. It’s output is directly connected to the main power-bank PCB. Even though the main PCB was dead, the pack itself was still good, reading 15.6V.

Since 18650 Li-Ion cells have higher cycle life than Li-Po, power banks based on 18650s should last longer. Their major downside is their bigger size due to them using cylindrical cells. My guess is that’s why they are uncommon nowadays.

Cylindrical lithium cells (18650 and 21700) are also common in power tool batteries and some household electronics, like portable vacuum cleaners.

That will be all. My congratulations if you made this far 🙂

Comments are welcome. I’m not really much of an expert when it comes to lithium batteries. Do correct me if I made any mistakes in this post. And excuse me for my language imperfections.