Looking for information on what sizes fit with minimum to no work done to force a fit. I have an 07, been running off the same 151r Super Start since I got the car in late 2021, with the battery having a sticker of April 2020(yeah, I'm surprised too. It will test good sometimes when getting an oil change, test bad others. It's unsure about if it wants to kis or live on lol). Wanting to upgrade to an AGM since I am going to be pushing around 1400w+ in my sound system. Currently doing around 1100w without issues(interior lights will flicker ever so slightly at volume of 30/40 with heavy bass songs, but otherwise no issues).
I've seen posts on reddit and other forums for the regular Civic that a 34 could fit with some work being done, but basically no information for the Hybrid on what would and wouldn't fit.

Looking to know any and all sizes that would fit that are larger than 151 & 51 offerings(both in terms of cca & rc)

 

51R is the largest practical requiring that you discard the shroud. Discarding the shroud increases exposure to heat and shortens the life of the battery. Given that it's capacity is about 50% more than the 151R, it has more margin, so you still get a little longer life out of them.

Having owned (including 03 HCH and 2X 06 HCH) and worked on hybrids for 15 years, I can say you really should reconsider your plans. These cars don't have alternators, and they charge from the DC-DC converter powered by the HV system buffered by the HV battery, particularly at anything but freeway speeds. A heavy electrical 12V load ultimately strains the hybrid battery. Given that the 06-08 HCH2 IMA battery is the second worst hybrid battery ever made, you're directly impacting vehicle reliability.