i dont think it matters as a fuse lets power through and will blow if the power goes over so its upto you i would go with 15-20 amp
Brand new from pedparts, motoforce racing pump I just had it hooked up to a 5amp fuse but that blew lol (12v pump)
Id just use a 2 or 3 amp personally though. 50 batteries are only about 4A so anything over 5 or so is probs a bit pointless