In modern passenger vehicles, the battery management system (BMS) and power distribution system are critical for ensuring reliability, safety, and performance. While MOSFET-based solutions are gaining traction in some applications, relays remain the mainstream choice for automotive battery main circuits. Here’s why.

1. Higher Current Carrying Capacity

Relays can easily handle hundreds to thousands of amps, making them ideal for high-current applications such as starting, load switching, and main traction circuits in electric vehicles. MOSFETs, on the other hand, generate significant heat at high currents and require multiple devices in parallel, increasing cost and board space.

2. High Reliability

Relays have simple, mature structures and have been proven reliable in harsh automotive environments—including high temperature, vibration, and electrical surges—for decades. MOSFETs are more sensitive to voltage spikes, static, and temperature, making them more prone to failure under demanding conditions.

3. Lower System Cost

Relays are cost-effective, especially in high-current battery applications, reducing overall system cost. MOSFET solutions require additional components such as drivers, heat sinks, and multiple MOSFETs, increasing manufacturing and BOM costs.

4. Lower Power Loss

Relays have very low ON-resistance (milliohms) and generate almost no power loss when conducting. In contrast, MOSFETs have higher Rds(on), causing noticeable power dissipation and heat at high currents.

5. Better for Harsh Environments

Relays are less affected by electromagnetic interference (EMI), voltage transients, or load dumps commonly found in automotive systems. MOSFETs require complex protection circuits and careful layout design to maintain reliability.

6. Higher Safety

Relays provide true physical isolation when open, ensuring safe disconnection in fault conditions. MOSFETs, as semiconductor devices, cannot fully isolate the circuit physically, which compromises safety.

7. Why High-End Golf Cart Batteries Are Becoming More Like Car Batteries

This also explains why your golf carts may experience unexpected shutdowns.

Even though golf carts are not passenger vehicles, they increasingly face conditions similar to light electric vehicles (EVs):

• High current loads
• Long uphill climbs
• Frequent impacts
• Strong vibrations
• High-temperature environments

As a result, using a MOSFET-based BMS (Battery Management System) gradually exposes several issues:

• Overheating
• False triggering of protection mechanisms
• MOSFET failures
• Reduced lifespan under high-current operation

In other words, the demands on golf cart batteries are getting closer to those of automotive-grade batteries, requiring more robust and reliable battery management solutions.

Summary

Relays offer clear advantages in high-current handling, cost-effectiveness, reliability, and safety, making them the dominant solution for passenger vehicle battery systems. While MOSFETs excel in fast switching and compact designs for low-power applications, relays remain the preferred choice for high-power BMS and EV battery management.