I am new to Bongo ownership and have a twin battery Bongo, ( twin engine battery, not leisure and engine

I have heard that these come from Northern Japan, where the weather is harsher, and as a result they are more likely to rust quicker, and have had a harder life etc.
Mine looks OK for it's age I reckon, but just interested:
What have folks got mainly, and whats the general view on these twin battery models ?