Suppose I have four AA batteries hooked up in series and I forgot about them and one of them eventually got completely empty due to self discharge. Also suppose that these batteries are not connected to any external circuit. Can that empty cell be reversed charge by the other cells?
My understanding of batteries is that the chemical reaction which releases the stored energy cannot proceed unless the batteries are connected to a load so that the electrons release by the reaction can flow through the external circuit. So in my example the batteries should be fine. But maybe something can occur in the empty cell that somehow make a current flow even though there is no external load to complete the circuit?
The reason for my question is that I am wondering if it is safe to leave four rechargeable NiMH batteries (in series to provide 5V) in an DIY device I built if I have a switch that disconnected the batteries from the circuit.