I want to power a diy 2.1 channel BT speaker. It can handle 18-48v power. I’m building one for a family member. Normally when I use this setup I’m constantly verifying voltage to not over discharge. But I’d like to have a setup where someone wouldn’t have to worry. My question is this. Wiring two Makita 18v 5ah batteries in series w/ two 3d adapter purchased from amazon. Which way is safest, protection board on each individual adapter or a 36v protection board on the combined adapters? I’ve read that the battery itself does not have protection only the tool. This came from a makita dealer.