Frank you would be better off running a mains powered small vac powered through an inverter. First of all there are many more of them made so the price is lower per unit. When you need a replacement there is more choice and retail outlets.
You do not need a huge battery. Run your vehicle engine to charge ther battery while the inverter is powering the vac.
This is one place where its best to buy a consumer product that really sucks. The 12V devices don’t hack it. 
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