Looks like a rodent. Isn't that bar on the battery metal? Put out some traps. I'd avoid poison since it's likely they'll just crawl in somewhere in the car and die. That area is right by the cabin air filter, so I wouldn't be surprised if it's nesting there.

 

It may be a rodent. But what about the plastic battery terminal covers and plastic front battery brace? It looks like someone use a grinder to remove some of the plastic, especially on the positive terminal.

 

You would be surprised at what rodents will chew on. If the OP looks hard enough, he will find oval/cylindrical mouse droppings.

This happens quite a bit.

 

 

OP get some more light on it and a higher resolution picture.

As stated, you would be amazed at what they will eat. On a motorcycle forum I'm on they eat through a dirty oiled air filter element having a METAL screen embedded in it and build a nest in the openings of the throttle bodies.... they are evil!
Seen one eat off a MAF sensor once too!

To me the covers look chewed but it is hard to tell by the lighting.

 

^^^^I played around with pict:




Lou

 

 

Rodent alright!

 

 

You set out traps, like I mentioned above. Either glue or regular metal traps, put a dab of peanut butter on them. Put them around your car, and in the engine bay. I'd advise against poison (such as d-CON) since it's all too likely they'll just crawl up into some nook and die there, stinking up the car and making it hard to find where they are.

 

From the close-ups of the damage, it does appear to be a rodent issue. Good luck there!

 

to my understanding rodents' teeth keep growing and to prevent them from over-growth they grind them down on anything that is around.
they are not necessarily eating the material!

 

looks like the problem is resolved since it doesn't look "fresh" since it looks like the person you bought it from covered the entire engine bay with armor all or some kind of protectant.
if you want to prevent further problems, spray deterrent such as vinegar or something strong.