My Store Bought BOSCH micron cabin filter #P3710 was $15.99.

For $42 ( cost me $40 2 years ago ) You can get a LIFETIME battery air filter.
( I think it was about the same price for a LIFETIME engine air filter too. )



Remember, the battery air filter is a low flow, low velocity, mainly a leaf and bug filter.
So while something of this quality is not required, for a little more cost, you'll never need to get another! Peace of mind and convienience is worth something! And no, no oil will get into the battery. #1 the filter placement is a long ways away, and #2 it is a low flow, low velocity air duct.