Best way for a relative newbie to drop 8v to 5V while maximizes available amperage

Thread Starter


Joined Oct 2, 2017
Hello, I need to take a powered USB hub (5v input from AC adapter) and power it from a battery pack. There are 13 ports on the hub and it will power 3 Raspberry Pis, an Arduino Mega, an Uno, 3 NodeMCUs. Relatively small devices with a max of about 500mA draw. I would like to plan for future expansion so I am thinking 5-6Amps max at 5v will work.

I have lots of 18650 batteries and I was planning on using some of them. Putting 2 batteries in series (app. 8v @1,500mAh) behind a 7805 regulator. This will give me 5v but only a max of 1amp.

If I repeat this with 3 additional sets of batteries - each set generating 5v @ 1,500mAh and use four 7805 regulators (one for each battery pack) can I then combine the outputs of the 7805 into one line to power the USB hub? Would that give me a.) 5v @ 6,000mAh, b.) 20v @ 1,500mAh, c.) a visit from the fire dept.



Joined Sep 9, 2010
You can get more amperage, but you’ll never improve the power efficiency. You’d do better to get a DC-DC converter. There are tons of them on eBay that can do exactly what you need at 90+ percent efficiency.


Joined Mar 14, 2008
Here's a typical cheap (likely Chinese) 5V, 10A buck converter, which should do what you want.
It claims over 90% efficiency so you should actually get about 30-40% more ampere hours @ 5V than the 8V battery puts out.