balsa model,
You are quite right and I have edited my post above to fix the error. I can't type as fast as I think apparently!
I defo agree that when connecting batteries in series it is possible to connect batteries of unequal capacity however it is best to use batteries of equal capacity. Also it is best practice to use the same battery type from the same manufacturer and all of the same age.
Dozens of times I have said to a truckie, "When you change one you should change them all" only to ignored and accused of trying to make another sale!
Cheers.