After carrying the heavy Boosted Board charger with me to work every day, I realized that I needed a 2nd charger at work. When I looked into getting a charger I saw that they were about $80 on Boosted's website. I thought that was pretty steep so I set out to find an alternative.
Because I've wanted a variable power supply to charge different batteries for quite some time, this gave me the excuse to invest the money in that instead of a Boosted Charger.
I picked up a 60W 5A power supply from eBay for $60.
There are less expensive ones, but I thought I should invest in one that seemed a little more well-made.
I also bought these barrel plugs. They are not the best quality, but they get the job done. They seemed slightly small to fit snugly into the boosted board plug so I wrapped the outside of the barrel with 1 layer of conductive tape.
Next, I measured the voltage coming out of my Boosted Board charger with a multimeter. 42.25V. The current is 2A per the label on the charger. The Boosted Board can charge at a higher amperage but I thought it was best to leave it at the stock settings.
I then set the max current by shorting the red and black plugs and setting the amps with the course and fine adjustment knobs at the bottom.
Here it is charging my board. As the batteries become charged, the voltage increases and the power supply slowly decreases the current without overcharging. (An analogy: If you prepay for gas and fill your tank, when it gets close to the prepaid amount the pump slows down.)
All in, I invested less than an OEM Boosted Board charger and I have something I can use on almost any battery.