/diy/ - Do It Yourself

Pic related. For the diodes, 1N5404 is probably good. For the resistor 2.2Ω 10W seems sensible. For the battery, 6 18650s in a 3S2P configuration, maybe 3S3P if you need more life out of them, 3S1P might be enough. If balancing is a concern, put some 4.3V zener diodes (1N4731) might prevent a fire. A better circuit using TL431s might be in order if you need something better.

Also pretty sure there's nothing in the router that can handle 12V but can't handle 15V.