Hi Mike, Say that two alcaline penlight cells have a capacity of 3000ma/h. You don't want that 3A over one hour but only 0,5ma during X hours. 3000/0,5 = 6000 (x 1 hour). Which is ca. 250 days, or ca 10 month, before the cells are empty. And empty is about 1.3v each. Good luck, At vW. >For example: if I have a circuit which will consume 450 uA >until the input voltage drops to 2.7V, how long can that sit >until it reaches 2.7V (assuming two 1.5V AA alkaline cells)? >Failing that, does anyone know where I can find equations >to solve? >Mike H. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body