DC:DC converter - Cheap, reliable and tested

[hydesigns]

I am building your project at the moment, but a useful tip for others doing the same - rather than using power from the first 2 cells (and potentially slowly unbalancing a small pack) although it doesn't specify in the datasheet - the Meanwell RS-15-5 works from 25V-370V DC - below 26v it loses regulation at currents over 1A. At low currents though, it will work down to 15V input!

Just connect the Vbat and Gnd connectors from the 4 pin plug from the JKBMS to the A and N pins (polarity is unimportant) to the Meanwell PSU.

And a weatherproof 8 DIN switchboard with a clear cover makes a perfect enclosure for the 4X20 LCD to be protected for outdoor applications.