It's NiMH, not Li-ion .....so no protection needed. And, 400 mah is the true mah rating, not overblown like most. I get a solid three hours out of one battery easy. They're cheap and work well for a 5 volt option IMHO.
On a side note, I see that battery junction has 1.2 volt 2000mah batteries with the side solder tabs. One just needs to stack four of these, solder the tabs and shrink warp the set to equal 4.8 volts with huge mah rating. Each battery is on sale for three bucks a piece here:
Tenergy NiMh 4/5 Sub C 2000mAh w/ TABS They also have a 30 amp high drain rating!!!! Dimensions are Height 32.5 mm, Diameter 22.25 mm. Would these fit the GGTS?
Never mind. RCR123a batteries are 17mm in width. The 22.5mm is too wide for GGTS.
These would be the ones to get. Dimensions are perfect for width
One 2/3 A 1400 mAh high capacity NiMH battery with Tab
Length is an issue though. 4 stacked would be 112 mm long. An 18650 is only 65mm long. You would need the Big Storm extension tube for it to work.