PV with Arduino and 12Volt Sealed Lead Acid battery
Size the fuses to the slightly more than max of what the controller can provide. 

The datasheet recommends this:


  It is recommended that no less than 2 times rated current fuse is
  connected with battery and load.


This would give the design protection from short circuits. 

The battery can support 5A so I'd use a 10A fuse. There is no rating for the load, so I would assume that 5A max for the load would be good (since that's what the battery can supply.) Use a 10A fuse there also and don't go over 5A for the load. I use car fuses (and holders) for my solar projects, they are available at auto parts stores.



Source:  https://midsummerenergy.co.uk/pdfs/ep5a.pdf