This got mentioned under another comment but it is worth stating at the top level: always use fuses or breakers in any kind of system, that battery is a fire/bomb waiting to happen if there is a dead short. Charge controllers can do this when they fail (I had a 30A MPPT CC do this, and not a cheap one). I wouldn't sleep next to this thing without it (I didn't look in incredible detail at their site but a cursory search didn't find anything about current protection).

DC systems and AC systems also require differently rated components. You cannot just go buy a 30A 120V AC breaker from home depot for the DC side of your system. It takes a lot more to disconnect DC than it does in AC (because AC cycles to 0V 60x/s it doesn't take much of a gap/insulator to break a connection, DC is not the same. Trying to use a light-switch for a DC light can result in problems [1].

I've had good luck with midnite products (charge controllers and breakers, etc) [2]. Their breakers are 100% rated in that if you expect your max current output to be 30A DC (12v probably), you can use a 30A breaker and not have to oversize it, they are rated to take the guess work out of how to size your breakers which is nice.

Edit: I tried to find some info on the CC they use (in case it had internal protection which I wouldn't trust even if they said it did) and no luck. Given its pedigree and price (most charge controller add on displays cost more than this thing) you definitely don't want to take any chances. Price doesn't always mean quality but there is probably a good reason they are usually more expensive than this.

[1] http://blog.gogreensolar.com/2015/02/ac-vs-dc-breakers.html

[2] http://www.midnitesolar.com/products.php?menuItem=products&p...