Yep, I am familiar with measuring current with a multimeter and have several in my shop. In considering battery draw down, the tricky thing is that the current won't be consistent. I assume there will be a peak flow when the shutter releases and an image is written to the card. This will make estimating the current draw over time a bit iffy depending on the shooting mode and settings, i.e. interval. motion detect, etc. My idea though is to get a rough estimate so that I can pick and choose from a selection of batteries with enough capacity to comfortably cover an anticipated time based on the nature of the surveillance project.