Can I use a Small Lead Acid Battery instead of a AGM Battery?

You won't damage the car, however this potentially may create a safety issue to the extent that if your car gets hit in the right rear fender and the battery case is impacted, you will have battery acid sprayed around the rear hatch and possibly into the rear seat area.

At minimum, make sure that the battery case has the positive terminal on the left side of the case when viewing the battery with the terminals on the side closest to you. If the terminals are reversed and you install the battery with the terminals adjacent to the fender, that constitutes another safety hazard to the extent that if that fender is impacted into the battery and contacts the positive terminal, an electrical short may result.

 

All the important features of a prius battery feature in passenger safety.

AGM means less acid to spread in a wreck.

Externally vented means less sulfuric acid and/or hydrogen gas in the cabin with passengers

JIS Posts are just odd, no US battery will fit them, you would need to replace the battery cables as well as the battery

Installation Kit for Optima battery in Prius

Here is a cheap 'correct' battery

www.amazon.com/dp/B010GKJ8F6/

 

Two excellent answers already.
Pay attention to what both of them said.

Nothing much else needs to be said.

 

Can you afford $152 + tax? Bosch makes an exact fit AGM battery for the Prius. This is superior to the Optimas.

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