The answer to your question depends largely on how your battery bank is currently wired, and also on your personal preference. Do you have a wiring diagram for your Meridian?
If the two batteries are simply wired in parallel (I am assuming of course that they are the identical make/model/size and the same age) then you can choose to use leave them wired together and use one battery disconnect switch to isolate the bank from the 12V distribution panel. Alternatively you can use two battery disconnects (
or one disconnect with 1-2-ALL functionality). This would allow you to isolate the batteries from one another, use either one individually, or pair them in parallel.
If by chance (as westend mentioned), there are devices wired independently to each of the batteries… and you choose not to remedy that situation… then you must use two battery disconnects.
In my TC I have a bank of three batteries and I have chosen to use three high-current battery disconnects (see photo below). This configuration allows for some flexability in how I manage charge and discharge and gives me the ability to isolate any one battery should it ever fail. It also means that I have the added task of manually setting (and remembering) which selection to use.

Cheers,
-Mark