Fit a battery in R-strap?

I've currently got the RS5. Though i like the storage, its a bit too bulky for me. Will i be able to fit an extra battery in the storage compartment of the RS4? It says its for memory cards, but I'm hoping i can squeeze in a battery.

The memory card fits pretty snug. I do not have my strap with me at the moment, but it would be a stretch (pun intended) to fit a battery in there.

I can squeeze an LP-E6 with the yellow protective cap thingy on it juuuust fine. Almost like the little pouch was -made- to hold that battery. I will warn you, however, wearing a heavy body/lens combo, the battery's edges/corners REALLY dig into your shoulder.

like wise, we have the double strap harness thing (forget the model) and the RS4, and with a 1dIV with a 70-200 2.8IS and a 7d with an 85 1.2L II mounted it's really comfy for.. the first.. 45 minutes;
gets annoying after 2-3 hours, and starts hurting after 8 hours (split the harness and just used 1 camera at a time, with it in hand most of the time to avoid irritating my shoulders anymore)

they work MUCH better than the regular straps, but they arn't a cureall to everything (don't expect miracles, but pretty damn close)

but yes, we store an LP-E6 for teh 5dII/7d in the RS4; its snug, and i worry about it falling out when the strap "breaks in" cuz its just barely fits lengthwise