kiev said:That's the number in the GS Yausa catalog on page 202,
https://www.gs-battery.com/wp-content/uploads/2016/09/GS-Auto-Cat-2015_web.pdf
The Japan standard terminals are smaller diameter, shown on page 16.
BTW there is some really good information in the appendices about testing, maintenance, and everything you ever wanted to know about lead acid batteries ∿
In the US we have a different numbering, BCI (Battery Council International) Group Size 151R
Thank you Kiev thats a great help. I have asked around about putting in an AGM battery but best advice seems to be replace it with what Mitsubishi had in first dat.