Maybe the 650 means 65mm.
Pete
Haaaa . . . You are so correct , and I thought I knew what I was talking about. Shows how much I use the Metric System ?
There was a battery I found that was bigger than 42120 that had the correct amphours.
Just a quick measuring will make it easy to find.
Doesn't really matter anyway.
If you are going to make a battery, just get enough of whatever cell you can get a good price on.
If you can find new lithium batteries cheaper than a $1 an amphour then jump on it.
Start here . . .
https://batteryhookup.com/