Somewhere in my travels across the Internet I ran into a formula for calculating transceiver usage and associated battery consumption. The formula has been a fairly accurate way to estimate my shack’s backup battery consumption. Draining 100% of a battery is obviously unworkable so transceiver run time is calculated at 75% of total battery amp hours. I have examples of the formula with both a 100 watt and 10 watt transceiver below. Plug in your own numbers and check your results.

Formula: %BAh / (((R%h x RI) + (T%h x TI)) = rt

  • %BAh – 75% of total battery ampere hour usage
  • R%h – percent of hour in receive mode
  • RI – radio ampere rating in receive mode
  • T%h – percent of hour in transmit mode
  • TI – radio ampere rating in transmit mode
  • rt – approximate transceiver run time

I keep an Optima Blue Top high performance AGM (sealed absorbed glass mat) battery on a CTEK Battery Minder Charger in the Ham Shack.

The AGM design holds the electrolyte in suspension and keeps the electrolyte in constant contact with the lead surface on the plates. AGM batteries are superior to flooded batteries in a number of ways. AGM batteries are spill proof, can be used in rugged environments, charge faster and have a much longer life to name a few.

Battery chargers are generally broken down into two general categories, smart chargers and trickle chargers. Smart chargers offer an efficient design to prolong battery life. Using trickle chargers for long term battery maintenance will actually destroy batteries because they cycle on and off which eventually overcharges and dries the battery out.

CTEK’s chargers switch to a pulse mode after the battery is fully charged. Pulse mode allows a battery to self discharge to a predetermined level and then another charge cycle is initiated. Pulse mode avoids overcharging and effectively exercises the battery as if it were in use. As a result, pulse mode greatly extends battery life.

I found that keeping my 5 year old Optima Blue Top maintained with the CTEK battery minder has done a great job in keeping my Optima Blue Top in peak condition.

50Ah battery with 100 watt transceiver

  • %BAh = 50Ah * .75 = .37.5Ah
  • T%h = 25% of hour = .25 x TI of 20 amp TX rating = 5 amps per hour
  • R%h = 75% hour = .75 x 3 amp RX rating = 2.25 amps per hour
  • 5 + 2.25 = 7.75Ah consumed hourly
  • 37.5Ah / 7.75Ah = ~ 4.8 hours transceiver run time @ 100 watts

50Ah battery with 10 watt transceiver

  • %BAh = 50Ah * .75 = .37.5Ah
  • T%h = 25% of hour = .25 x TI of 2 amp TX rating = .5 amps per hour
  • R%h = 75% hour = .75 x .25 amp RX rating = .15 amps per hour
  • .5 + .15 = .65Ah consumed hourly
  • 37.5Ah / .65Ah = ~ 57 hours transceiver run time @ 10 watts

What kind of Ham Shack backup battery system do you use?