I know this has been covered before but I can’t find the thread.

I’m in the process of cladding the outside of my single skin cement block garage. The reason im doing this is because I’ve noticed a bit of moisture bleed through when the gutter has overflowed but also for aesthetics.

My question is should I fit a DPM behind the vertical batons before fitting the cladding? If so, which should I use?

Forgot to mention I’m using tanalised shiplap T&G.

When I did mine I struggled to find conclusive info. In the end I put some breathable membrane up under the battens. It was cheap and easy (a couple of roll ends from eBay). Been bone dry inside since

Yes, you should.  Tyvek or Proctor roofshield or similar would be fine.

Yep, breathable paper like tyvek as above.

You also need to maintain the airgap that you are correctly creating with the furring strips allowing air in at the bottom and out at the top.to dry the back side of the wood when it gets wet.

You could go crazy and take the opportunity to insulate the exterior walls too!