I have posted how to calculate battery life here before. John gave a pretty good reply, but there are a couple of other points that should be made.
1. A lead acid battery is rated assuming the current is drawn at the 20 hour rate. If you draw more current than this, you will get less capacity from the battery. At the 10 hour rate, the capacity is diminished by about 10%, at the 5 hour rate it is diminished by 25%, and at the 1 hour rate it is diminished by 40%. 2. It is difficult to fully charge a lead-acid battery by trickle charging it at a constant voltage. Trickle charging at a constant voltage will only restore about 85% of the battery's capacity. To do better than this you need to use one of the "smart" chargers or triple mode charges such as those based on the Unitrode (now TI?) 3906. If you do not realize this you can get substantially less life from the battery than you anticipate. My K-1 draws about 70 mA on receive with the headphones and volume set for comfortable listening in the field. The transmitter draws about 1.1 A on transmit. With half of the time spent listening, and half of the time spent transmitting with a 40% duty cycle I get an average current draw of 0.276 A. If you constant voltage charged the battery, you will have a 20 hour capacity of 3.4 AH. At a current draw of 276 mA, I am pulling current out of the battery at a 12 hour rate. Since this is greater than the 20 hour rate our capacity will be diminished by about 10%. Reducing the capacity by this amount leaves 3.06 AH capacity. Dividing by the average current draw, 0.276 A, we get 11 hours capacity. Of course, in actual operation the average current draw can vary quite a bit, usually on the down side (we forgot to include bathroom time and emergency antenna repairs in the above calculations) so it is best to only use these numbers as a guide and not to really expect to get that last hour or half hour out of the battery. I hope that this helps. - Dr. Megacycle KK6MC/5 ______________________ James R. Duffey KK6MC/5 Cedar Crest NM 87008 DM65 _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net http://mailman.qth.net/mailman/listinfo/elecraft You must subscribe to post. Subscriber Info (Addr. Change, Unsub etc): http://mailman.qth.net/subscribers.htm Elecraft page: http://www.elecraft.com