The key difference between a starter battery and a regular battery, such as a semi-traction battery, lies in their design and the function they serve. Here are the main differences:

1. Design: A starter battery, also known as an SLI (Start-Lighting-Ignition) battery, is designed to provide short, intense bursts of power to start a vehicle. Starter batteries have thin and superficial plates, which result in a large surface area and rapid power delivery. On the other hand, regular batteries, such as semi-traction batteries, are designed to deliver power over an extended period, often during a deeper discharge.

2. Power delivery: Starter batteries are optimized to deliver a high power output for a short period, which is necessary to turn over a vehicle's starter motor. Regular batteries, like semi-traction batteries, are capable of providing more consistent power delivery over a longer period.

3. Capacity: Starter batteries generally have a lower total capacity than regular batteries. This is because they are primarily designed to provide short, intense bursts of power for starting a vehicle. Regular batteries often have a larger capacity, which means they can store more energy and deliver power over an extended period.

4. Deep discharge: Regular batteries, such as semi-traction batteries, are better resistant to deep discharges and repeated charging, whereas starter batteries are not designed to be regularly deeply discharged. Deep discharge can significantly shorten the lifespan of a starter battery.

It is important to choose the right type of battery based on the application. Starter batteries are ideal for vehicles where short, intense power bursts are required, such as cars, motorcycles, and boats with starter motors. Regular batteries, like semi-traction batteries, are more suitable for applications where a long-term power source is needed, such as marine applications, recreational vehicles, caravans, solar energy systems, and electric vehicles.