New keypads for entry gates at self storage business

I'm trying to figure out if I can deduct the cost of getting new keypads at the entry gates to our self storage facility, what is the most depreciation I can take.  When setting it up as a new asset in Turbotax Business (filing a 1065 return), if I select rental real estate then security systems it trys to depreciate it over 39 yrs and limits the section 179 deduction to business income so the deduction is next to nothing because all our income is rental income, not business income.  Does anyone have any suggestions?