A 155 car battery is typically fitted to a Toyota Prius, but it doesn't just come in one shape and size. Be sure to check your owner's manual before committing to a new one so you know it will fit.
As with all types of car battery, the 155 can vary slightly depending on its intended model. Some, for instance, have smaller terminal posts than others, so it pays to do your research before you buy.
The size of the gas vents can vary from model to model but this is easily adjustable if it turns out to be too big.
The old, dead battery in your car should tell you the exact dimensions you need for the replacement. If you are unable to find them, consult a mechanic or the manufacturer to find out more before making a purchase.