I have found what I think is a neat and simple way to store a multiple of batteries within a BattleGrip pistol grip.  (great suggestion SMGLEE).   I line up a multiple of batteries separated by spacers within a piece of heat shrink tubing and then heat shrink the batteries together to make a stick.  Use a tubing diameter which just receives the baterry diameter.   The Spacers are pieces of earplug foam or cotton balls located between each battery to provide separation therbetween. After heatshrinking each battery can be squeezed out individually by squeezing between the last battery in the stick and the next one.  Alternatively, each battery can be cut out.  
The battery “stick” is stored as normal. Works quite well for the battle grip as a large number of smaller (aimpoint batteries) can be stored in a single AA compartment without rattling.  That is, you can stack 4 or 5 aimpoint batteries to make a stick which fits into the AA length compartment without requiring the foam spacers in the battlegrip.  [let’s see, 10 batteries X 10,000 hrs or battery life each in an aimpoint =  a hell of a long time.  
Should simplify battery storage in Crane and Vltor stocks…
Try it.  
What do you think?