I want to add a bit of CR123 storage to my rifle without adding 6 oz of stock weight. I also like the A2 grip angle so with that being said is the TD BG 16 a good choice? It looks like the only difference between it and the 17 is the extra polymer at that curves around the rear of the bottom receiver? Any other good options for CR 123 storage besides stocks? 

The MagPul MIAD with the small backstrap and finger bump front strap is basically an A2 grip with storage capability. You can mix and match to configure the grip as desired.

The Tango Down has a similar grip angle, but the shape of the grip gives it a different "feel" when holding the rifle, the swell and curves "force" your hand into position with the TD. This is good for some, not as good for others.

To answer your question, however, yes, the difference between the 16 and 17 is the backstrap/"beavertail."

~Augee

If you want to stuff a couple in a grip, the Magpul CR123 grip insert is GTG (and is sealed with waterproof rubber cap).  
The TD grip storage design is less secure, IMO.  However, TD makes forward grips that have sealed storage compartments that are excellent.  
The standard size should hold 2 CR123s, and the stubby will hold 1.

So I picked up a couple of these guys and have found them to be precisely what I was looking for as far as angle and feel of the grip. I also tried out a VLTOR clubfoot IMOD for storage and added 3 CR123s to it and am finding the weight to be not bad at all.