This is what I use in both my 3rd Gens. It works well as long as you remember to turn it off. No more battery drain.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
When people say it's not a big deal because it draws very little power, i guess it depends how long your vehicle sits between starts. If you use your rig everyday, probably not a big deal. If you let your rig sometimes sit for a week or two, maybe it is a big deal. The other thing I like about the on/off switch is it gets the ODB II reader to a different more secure location. I have mine velcroed in the cubby under the ashtray. The OBD II port points downward so gravity is working against you. On a bumpy fire road, my reader fell out before I had the switch installed. Also, with it dangling there in the reader port, I accidentally bumped it with my foot a few times making me think one day I'm going to end up braking my OBD II and/or the reader. So, the switch does more for you than just preventing you draining your battery.