Yes! They are 4 1/3 A NiMH cells all shrink tubed together. They run at about 4.8 volts and last a good long time..
Sounds similar (and perhaps identical) to the 5V custom batteries sold by electronicstix for the Mako Maksi. Four 1.2V nimh cells stacked in a plastic shrink wrap, light green colored. 400mAh total capacity.
They're well-manufactured, nice batts. Nominal voltage is 4.8V, but they charge to 5.6V initially, quickly settle back to 5.1V, then gradually diminish to 4.8V.
If these custom batteries had a number designation, they'd be called 14650s, since they're 14mm in diameter and 65mm long. They work beautifully in 18650 tube or box mods. I always use them in my Phidias wooden bottom-feeder and sometimes in my Omegas and MaxiRoughStack tubes.
Most 18650 Li-Ion batteries are actually 1-2mm longer than their designated 65mm, presumably because of the protection boards, so these 5V custom batts are a little shorter than 18650s. They usually fit, however, and work with spacers or washers when they're a tad short. Since they're 4mm slimmer than 18650s, I made tape-wrapped cardboard tubes they slide into to increase their diameter for a more snug fit in the battery slots.
At only 400mAh, these babies can't be expected to provide long
vaping runs before needing to be recharged. 3-4 hours of moderate vaping at best. In my experience using them, performance doesn't gradually deteriorate, however. They vape nicely right up to the point of exhaustion, when they just quit all at once. They have no over/under protection cutoff circuitry, but, since they're NIMH chemistry (safer), don't need it.
And yes, they do require a special low-drain charger. A full recharge takes 4-5 hours per battery, so having multiple backups is effectively required. I own five of them. The relatively brief run times don't bother me at all, though. I like them.