Can I Use an RTR Mod 72V 35Ah or Touring 72V 45Ah Battery on an ETM RTR Alpha?

Short Answer

No.

The ETM RTR Alpha is designed around an 81V nominal battery system, while the RTR Mod 72V 35Ah and Touring 72V 45Ah batteries are 72V nominal battery packs.

Installing a 72V battery into an RTR Alpha will result in significantly reduced performance and is not recommended.

Understanding the Difference

ETM RTR Alpha Battery

The RTR Alpha uses:

• 81V Nominal
• Approximately 92V Fully Charged

This higher battery voltage is a key part of what allows the RTR Alpha to deliver its performance.

RTR Mod Battery

The RTR Mod battery is:

• 72V Nominal
• Approximately 84V Fully Charged

RTR Touring Battery

The RTR Touring battery is:

• 72V Nominal
• Approximately 84V Fully Charged

What Happens If I Install a 72V Battery?

The bike will power on and operate, but performance will be reduced.

Because electric motor power is directly related to voltage and current:

• Lower voltage results in lower peak power
• Lower voltage results in lower motor RPM
• Lower voltage results in lower top speed
• Lower voltage reduces overall acceleration

The controller can only work with the voltage available from the battery.

Performance Impact

When using a 72V battery on an RTR Alpha you can expect:

• Reduced top speed
• Reduced acceleration
• Reduced peak horsepower
• Reduced motor RPM

The bike will no longer perform at RTR Alpha specifications.

Low Voltage Protection & Battery Tapering

One of the biggest issues is that the RTR Alpha controller is tuned around the 81v nominal battery.

The controller has been programmed with a low-voltage cutoff and tapering strategy designed to protect the 81v battery from over-discharge.

As battery voltage approaches the low-voltage limit, the controller begins reducing available power.

This process is commonly referred to as:

Low Voltage Tapering

The goal is to:

• Protect the battery
• Prevent excessive voltage sag
• Prevent unexpected shutdowns
• Extend battery life

Why This Creates a Problem

The RTR Alpha controller expects to see voltage values associated with an 81V nominal battery.

When a 72V battery is connected:

• The fully charged voltage is already significantly lower
• The controller sees lower battery voltage immediately
• The controller believes the battery is much closer to empty than it actually is

As a result:

• Power limiting may begin prematurely
• Performance may be heavily restricted
• Battery percentage calculations may be inaccurate

In severe cases, the controller may behave as if the battery is nearly discharged even when the battery still has substantial charge remaining.

Why Does the RTR Alpha Use an 81V Battery?

The RTR Alpha powertrain was specifically designed around the higher voltage battery platform.

Benefits include:

• Higher peak power output
• Increased motor RPM
• Improved acceleration
• Higher top speed
• Better overall performance

The battery, controller, and motor were all engineered to work together as a complete system.

Recommended Battery Options

For optimal performance, use:

• ETM RTR Alpha 81V Battery
• Approved replacement ETM RTR Alpha battery packs

These batteries provide the voltage required for the controller and motor to achieve full RTR Alpha performance.

Bottom Line

While a 72V RTR Mod or Touring battery may physically connect and operate the bike, it is not the intended battery for the RTR Alpha platform.

To achieve the advertised performance, power output, acceleration, and top speed of the ETM RTR Alpha, an 81V nominal Alpha battery should always be used.