Understanding the Charge Limits of the YAESU FT-70D / FT-70DR Two Way Radio

The YAESU FT-70D and FT-70DR are popular dual-band handheld transceivers that operate on both analog FM and C4MA digital modes. Like all lithium-ion powered devices, understanding the proper charging limits is essential for maintaining battery health, ensuring safety, and maximizing operational readiness. This article explains the charge limits and related specifications for the FT-70D/FT-70DR radio.

Charging Voltage Limits

The maximum charging voltage for the SBR-24LI battery is 8.4 V. This is the critical limit that should never be exceeded.

As a lithium-ion battery, the SBR-24LI requires a constant current/constant voltage (CC/CV) charging profile. The charger must regulate voltage to exactly 8.4 V during the final stage of charging to safely reach full capacity without overcharging the cells.

Why This Limit Matters

Exceeding 8.4 V can cause lithium plating, internal short circuits, thermal runaway, or fire

Charging below this voltage will result in incomplete charging and reduced operating time

Quality chargers automatically stop when the battery reaches 8.4 V

Charger Options and Their Limits

SAD-18B (Standard Charger)

This is the supplied battery charger included with the FT-70DR. It is designed specifically for the SBR-24LI battery and automatically observes the 8.4 V charging limit.

SBH-28 (Rapid Charger)

An optional rapid charging cradle is available (model SBH-28) that provides faster charging while still respecting the 8.4 V voltage limit.

SAD-24C (Alternative Charger)

The SAD-24C is an impulse-type power supply compatible with the FT-70DR, providing a fixed output of 12 V DC at 0.5 A. When using this or any third-party charger, verify that the charging circuitry correctly limits voltage to 8.4 V at the battery terminals.

⚠️ Important: Never connect a charger that outputs more than 8.4 V directly to the battery. Only use chargers specifically designed for the SBR-24LI battery or the FT-70D series radios.

Charging Safety Precautions

Use only YAESU-approved chargers — or third-party chargers explicitly designed for the SBR-24LI battery with proper 8.4 V termination.

Avoid overnight charging with unknown chargers — While the standard charger includes automatic shutoff, inexpensive aftermarket chargers may not.

Do not charge a hot battery — If the battery is warm from heavy use or high ambient temperatures, allow it to cool to room temperature before charging.

Monitor for swelling or damage — Discontinue use if the battery pack shows any signs of swelling, leakage, or physical damage.

Charge in a fire-safe location — Place the charger on a non-flammable surface away from curtains, paper, or other combustibles.

Battery Life Expectations

The SBR-24LI battery provides approximately 7–8 hours of typical use under normal operating conditions, based on a transmit/receive/standby cycle ratio. User reports indicate actual battery life can be shorter with heavy digital mode use, with some operators reporting as little as 2 hours of continuous operation.

Tips for Maximizing Battery Charge Cycles

Avoid fully discharging the battery regularly; lithium-ion batteries prefer partial discharges

Store the battery at approximately 40–60% charge if not used for extended periods