Open source 12V powerbank

Why did I build a power bank?

Why would anyone even try to build a power bank – i.e. an external battery for charging mobile devices – these days? These things are commodity, it’s impossible to compete. Right? Well, that is until you find out that the type of power bank for your application, namely charging a higher-end tablet with 12V input, does not exist cheaply. Looking around for 12V power banks yields a lot of li-ion car jumpstarters (*) and very few actual power banks. Those that exist are pretty expensive and often don’t even perform that well. Let’s run down the list:

Name (linked)	Capacity	Price	Comments
(no-name) Portable PowerBank with 12V & 5V USB	Approx. 90Wh	$71.99	Big and heavy: weighs 650g. Output power 60W max. Seems to actually be for solar applications. Very little information.
XTPower MP-10000 with dual USB and DC 9V/12V 2A	37Wh	$59.90	Output is limited to 2A. Auto turn-off is nice. Weight is ok (300g). Includes lots of connectors.
RAVPower Xtreme 23000mAh	Approx. 85Wh	$99.99 (normal: $299.99)	Pretty big and heavy (600g), very nice design. Super expensive. High output power.
Qualcomm BlitzWolf QC2.0	Approx. 35Wh	$26.99	Low output power (12V/1.35A), uses QC2.0 instead of general purpose output

(*) Car jumpstarters will not work, because they have a 3S pack of li-ion cells directly connected to the output, meaning the output actually varies from about 10-12.6V. My tablet (Cube i7 Stylus) and the Microsoft Surface series only accept 12V +/- 5%

Prices exclude shipping. I tried my best to include an example of every ‘category’ of available power bank in this list, but there are obviously hundreds. They fall into four general categories:

1. QC2.0 chargers, which use the new Quick Charge protocol to deliver 5-12V at up to 18W to supported mobile devices. These are the only ‘cheap’ 12V power banks, but unfortunately also woefully underpowered as well as using a communication protocol on the charging port. That makes it very hard to use as a generic 12V charger for a tablet.
2. Ridiculously expensive chargers. There are a bunch, and they all retail for between 100-400 dollars. Some are specifically marketed towards high-end laptop/audio/photographic gear. They do have really good specs (often up to 4-6A outputs and variable output voltage), but are also generally heavy and very proprietary in their connections.
3. ‘Almost there’ power banks. There are a lot of 12V/1.5A and 12V/2A power banks in the $60-100 price range. Unfortunately, I need 2.5A to be able to charge AND use my tablet and $60 is a bit on the high side, especially with more than $15 shipping (to Europe). Locally, these tend to retail for €100+.
4. Weird application-specific stuff. I put in a solar charger. Often without satisfactory documentation

So, how do we fix this? Well, build your own.

Read more: Open source 12V powerbank