I have a custom made 5s power bank (30 x 18650 cells) and I want to make a power supply to charge my laptop using this power bank. It's not a big deal to make a 5V charger because I just have to hard wire a 5V step down regulator and it will work, but what about higher voltages?
Of course, I can use a standard AC power supply and connect it using a car power inverter, but efficiency in this case will be quite low. I tried to find such power supply/controller on aliexpress or ebay, but it looks like only 5V versions are available. What is the best/easiest way to do it?