So that's your pitch, no vent? All modern VRLA batteries are fully recombinant and that vent is only for safety (see for example https://www.gsbattery.com/cont

So that's your pitch, no vent? All modern VRLA batteries are fully recombinant and that vent is only for safety (see for example https://www.gsbattery.com/content/vrla https://www.gsbattery.com/content/vrla). It requires no maintenance, inspection, or installation accommodation according to any manufacturer's recommendations I can find. And unfortunately, lithium-ion cells have vents, too, for the same reason: to limit the risk of explosion due to overcharging or cell defects. See among many other examples http://batteryuniversity.com/learn/article/lithium_ion_safety_concerns http://batteryuniversity.com/learn/article/lithium_ion_safet.... You can find discussions of venting in these cells in articles about Boeing's problems with the Dreamliner batteries. I can see no material distinction here. Even if I were to accept that the vent design in Li-ion cells is superior to that of VRLA designs, it wouldn't justify paying twice as much for the same capabilities.