Review on USB Rechargeable Lithium D Batteries - 1.5V / 4000MAh (2-Pack) - ECO-Friendly & Recyclable - No Memory Effect - Not NI-MH/NI-CD/Alkaline Batteries by Lisa Frank

I'm mostly happy with these. The only con I've seen is that they have some connection problems. They don't seem to be exactly the same size as a D cell, so they wiggle around (in a mag light in my case.) This causes the connection to be intermittent unless I adjust the spring in the base of the light to make it a tighter fit. If I buy more lion batteries, I'd definitely move in the direction of the ones with a micro USB charge porton the side instead of these that have a removable cap and full size USB-A port.