I recently had a problem with my AGM Optima Yellowtop battery being drained by an inverter that was connected full-time to it. After resuscitating the "dead" battery, delegating the inverter to "connect when needed" status, and putting a master cut-off switch between battery and fusebox, I had no power drain at all. The battery has stayed at 12.8+vdc for over a month now. However, I neglected to hook-up the constant 12vdc feed to the Pioneer stereo that keeps pre-sets and the clock in memory. I ran a new wire to the terminal strip prior to the master switch, unfused, and got the memory reset. Tested it after 6 hours with switch off...memory intact. I used my multimeter to check the amperage draw incurred by constant feed for the memory; it was drawing between .01 and .02amps (fluctuating). Say an .015amp average. That = .18watt. Not much. I wanted to see how long it could run on my 55ah AGM, not wanting to have a dead battery situation again, so I used this calculator
http://ep.yimg.com/ty/cdn/sports-imports/BatterydrainCalc.html and came up with this figure 1527.77 hours (or 63 days, 15.77 hours). I think I'll have a little wiggle room on watching the battery life, if that's all the drain I have to worry about.