What makes the HT200ET heat tolerant?

Five named pieces of engineering. The Helios additive reduces float current by up to 75 percent, and float current is what generates internal heat and dries cells in a hot room. The Microcat catalyst lowers it further and mitigates thermal buildup. The TempX grid alloy resists the corrosion that accelerates at temperature, the THT case plastic is formulated for heat and holds plate compression, and IPF plate formation keeps cells consistent so no single cell runs hotter than its neighbors.

Why does a heat-tolerant battery still publish its ratings at 77°F?

Because 77°F is the industry reference temperature, and publishing to it is what makes ratings comparable across manufacturers. Heat tolerance shows up in service life at your actual room temperature rather than in the capacity table. Every lead-acid battery ages faster above 77°F; the Fahrenheit engineering slows that penalty rather than repealing it, so a string in a 95°F shelter lasts meaningfully longer than a standard VRLA would in the same room.

Can I draw the full 190 Ah in one hour?

No, and the spec table says so: the 1-hour rate is 144 amps, which delivers 144 Ah, against 190 Ah over the gentler 8-hour discharge. Lead-acid capacity always shrinks as the draw rate climbs. Size the string from the rate that matches your reserve-time requirement, and if your discharge window is under an hour, tell us and we will check whether a high-rate series such as the Unigy HR fits the duty better per dollar.