Warmest undergarment available?

[GDimery]

SANTI Extreme BZ400 with heated vest! I dive in 34*F water with that and I am good for a 90 min dive. The only way to go. M2M as well which is an added plus

 

[lacdenis]

SANTI Extreme BZ400 with heated vest! I dive in 34*F water with that and I am good for a 90 min dive. The only way to go. M2M as well which is an added plus

Which heated vest do you wear? I've been diving 52 degree water in just a 7mm for 4 1/2 hours at a time (three dives at 30') and get to the point where I can barely depress the inflator. I'm adding a Lavacore layer this time and I want to add a heated vest. Are you using the UTD or something else? Battery recommendations for this period of time? Thanks.