This thread is right up my alley. I use these. Less than 3 bucks each
https://www.ebay.com/itm/19566854385...Bk9SR6Dv1_KJYg
Not necessarily from this particular vendor, but just search for "5 LED USB Rechargeable Bike Tail Light". Include results from China, Hong Kong, Taiwan. Yes, they're from China and take about a month to be delivered, sometimes less.
I get one red and one blue light to "simulate" cop lights. I use the 4th setting. Not too busy, not too stale. And yes, I'm about 90% positive they're legal in my area because I've checked the statutes. Also, I've been passed by many cops in the area and no one has said anything,
Use the micro usb that's included. Gently insert and take out. I've broken a light by applying too much pressure. My rides are for about an hour and a half, maybe more. I recharge every 3 rides. I could probably get 4.