(Reuters) - The National Highway Traffic Safety Administration said on Wednesday that it closed a preliminary investigation into about 1.8 million Toyota RAV4 SUVs over concerns related to short circuits in battery terminals.

The probe focused on contributing factors and frequency of fires originating from the battery region in the engine compartment in RAV4 crossovers from model years 2013-2018, the U.S. auto safety regulator said in a statement.

"The reported fires took place in vehicles known to contain aftermarket batteries or whose age exceeded the expected life of the original equipment battery," NHTSA added.

The regulator identified a few parts in the engine bay as the main factors causing the contact between the battery hold down bracket and the positive terminal of the 12V battery.