Solar Power Newbie question

I got my MPPT controller in and read the instructions (I hope I wasn't treading on dangerous ground here;) ). It says I should put an in-line fuse holder between the controller and the positive terminal of the battery. The problem is it doesn't say what size fuse I should be using. Does anybody know what size??? I have one 250 watt, 8.7 Amp solar panel and a 20A controller and I'm hooking to two 12V marine batteries wired in parallel to maintain 12V. Also, since I'm going to a battery I'm guessing I could get a part like that at the car parts place like Auto Zone, or will I need to go to the RV dealership?

It's sure nice to have a place like this to go for help . . .THANKS!

Thanks to both of you for your prompt and easy to understand responses. I can't wait to get this thing in and on, which won't be for a couple weeks at least.

Nope not a problem. Just wire controller directly to battery as described in your instructions (would suggest you hook positive to one battery and negative to the other battery to ensure balance and full charging of both batteries)

Hooking direct to battery also has the advantage of the solar charging works rather the batter disconnect is on or off making it an outstanding battery maintainer when in storage, never have to worry about your batteries expect to water them occassionally.

No conflicts. Just add the solar direct on the battery and enjoy.