Maximize your Handlheld VHF Radio's Battery Life E-mail
Written by Allen Sansano   
Sunday, 28 April 2013 12:42

m72 A handheld VHF radio is an indispensable tool for kayak fishing adventure travel, for angler to angler communication, listening to weather forecast, or a lifeline in the case of an emergency. When selecting a handheld VHF radio for these circumstances, two features are at the top of the list. First is a long battery life. Often times one will not have access to a regular charging source, so having a handheld VHF radio that can last up to a week becomes that much more important. The other feature is a high transmit power. 25 watts is the maximum transmit power for 'fixed' VHF in the US and handheld VHF's typically top out at five to six watts max. All handheld VHF radios also allow access to weather broadcast, giving one up to date information to the region where one is fishing and usually have "one button" access to channel 16 for emergencies.

If one looks at published specs, you'll see that some handheld VHF radios are rated for up to 16 hours of operation, with many having much lower ratings. How then can one stretch a handheld VHF radio's battery for up to a week?  Here at Kayak Fishing Magazine we selected the Icom IC-M72 as our preferred handheld VHF radio. We'll use specs from that model to explain the method behind our choice.

Published VHF Battery Life

It is common in the industry to measure Handheld VHF radio battery life under the following conditions, 5% transmit time, 5% receive time, and 90% standby time at maximum transmit power and receive (speaker) power. The IC-M72 is specified to have 16 hours of battery life. This unit also has a battery rating of 200 mAH. At 6 Watts transmit, it consume 1700 mA of current. At 500 mW speaker output, it consumes 400 mA of current. Using the above number, it can be calculated that the IC-M72 consumes 22.2 mA in standby.

Increasing VHF Battery Life

The above numbers suggest that 1360 mAH of the 2000 mAH battery are consumed by transmit mode. To increase battery life, use your VHF in the lowest transmit mode for general communications. All handheld VHF radios have a 1 Watt transmit setting. In this setting the IC-M72 consumes 700 mA of current. Calculating battery life under this condition results in ~26.67 hours of life, and increase of more than 10 hours. Keep in mind that your radio is now set to 1W transmission; in an emergency situation where maximum transmission is necessary, remember to switch it back to 6W transmit power.

Aside: please note that using a battery pack of AA batteries reduces your transmit power to effectively 2W due to limitations in the current-providing capacity of AA batteries.  Therefore, we do not recommend using the AA battery pack with the intent of changing batteries when on a kayak fishing adventure.  You will not NOT get full transmit power with that configuration.

To further increase battery life, one should not set the speaker volume to the maximum. At maximum volume, the IC-M72 is actually too loud for normal kayak fishing ambient noise level. By setting it to 1/2 volume one can reduce the receive power consumption by more than 1/2 as it is not a linear relationship between volume and power consumption. But even assuming halving the power consumption of the speaker, one can increase the battery life to more than 30 hours!  Turn your volume down.

Talk Less

Keep in mind that 5% transmit and receive time at 30 hours is about 1.5 hours of transmit time and 1.5 hours of receive time, which is a long amount of time. With 1W transmission and 1/2 speaker power, the power while transmitting still accounts for more than 1/2 of the battery consumption. Total transmit power can be reduced by talking less. Your average message likely needs be but a few seconds. By staying conscientious of your transmission time, it is conceivable to use less than 3 minutes a day transmitting. Under these circumstances, one can increase battery life to almost 6 days, assuming a 10 hour day, while still maintainin 30 minutes of receiving time per day (for listening to the weather and or random radio traffic).

Listen Less

With all the above optimizations in place, your tranmit power is now ~10% of the battery life, your receive power is more than 25% of the battery life, and the rest of your battery life is standby. By reducing your total listening receive time to 9 minutes per day, one can realize a full week (10 hours per day) of battery life. Have your buddies talk less and listen to the weather forecasts less, or share weather listening duties between the other handheld VHF radios so only one radio gets used for that purpose per day.

Using the above methods we have shown how one can increase the effective battery life of a VHF radio from less than 2 days to up to a full week.

 

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