Timely thread for me. I just had multiple conversations with battery makers at SEMA including Anti Gravity and Braille. I started my build with the Braille AGM 21, but it is on the limit of what it can handle and drops below minimum power too fast on my setup after a few cranks.
Nice to hear that the GU1R is doing the job as that is the one I will probably upgrade to, plus its only slightly larger than the Braille AGM which means it will fit in the only space I have to put it. I think its 500-600 dollars, not cheap, but if that's what it takes not to be stranded somewhere - it is worth it to me.
The Braille rep said the L is twice as strong as the AGM although the specs don't really say that, since you have both batteries what is your take on cranking power and reserve power between the two?