Running two different AH batteries together?

[Cuppa]

just a quick note . I was told when joining batteries to have positive on one battery and negative on the other for charging as this creates the vision of one large battery

I expect you are referring to connecting two batteries together in parallel (i.e. keeping the same voltage of a single battery whilst increasing capacity). If so your informant was correct & it looks like this. You can connect loads to just one of the batteries, they will still charge & discharge as one, but the pictured method is considered better (although I’m not exactly sure why).



If connecting more than two batteries together in parallel there are several ways to do this, the article here suggests which are the better options.
In my Patrol the three aux batteries are connected in the star pattern (Method 3 in the above link) similar to this: