You lose a lot of the benefits of the little Bandit with the big SLA battery. I sent these pictures and links to the OP. You can swap in an 8 battery pack and use rechargeable AA's in it. I use plain Alkaline AA's and buy them by the 100 pack and carry a spare battery pack in the caller bag.
This year I found an eight AA battery charger that has a USB plug on it that I can plug into the solar system on my hunting truck and charge batteries at night while I'm camped out.
This one has the same internal external speaker switch as the OP's and there is still room for the eight pack