Does battery self discharge when connected? I am an electric engineer, and I read about battery self discharge phenomenon. I was wondering whether a battery self discharge rate is the same when it is unconnected (i.e. in storage) and connected (i.e. when it is plugged into a device and being discharged "normally").
In other words, when I calculate battery life time for a product, should I take add the rated self discharge of a battery to the general current calculations or not? And also-is the answer similar to all types of battery?
Great question! I studied battery chemistry as part of my graduate work, and I think the answer depends on the mechanism of self-discharge. 

I think that by discharging the battery through an external circuit, you will generally cut off the self-discharge mechanisms (depending on the discharge rate), so if you add the discharge rate and the self-discharge rate, you will probably underestimate the battery life. You should also keep in mind that the rate of self-discharge depends on the state-of-charge for the battery, and is generally worse at high state of charge. Thus, even the manufacturer specification for self-discharge rate isn't a constant.