I found a group 51 battery that looks very promising. Thanks Chris.
I stared at thermal greases (& my phone) at Frys before deciding the PTU grounds through its heat sink, so I found deoxit grease that contains copper particles (L260Cp). Unlike arctic silver, it looks like this deoxit grease will consistently conduct electricity. I'll be playing with my multimeter during install regardless.
I don't necessarily want to switch to bolts to secure the PTU because the screws will keep me from drastically over torquing.

