Yes you can leave them there, but if you look at the storage recommendation for the batteries that would not be recommended, the batteries should be stored at half charge, leaving them on this charge would keep them at full charge. I have two of these and when I know I am going to be working in the shop the next day, I will load them up the night before and will have 12 fully charged batteries by the morning. Enough to keep me running for a long time.
One at a time, but put all the batteries you need charged into it and it will go from one battery to the next until they are all charged.
I know it is not recommend to keep the batteries in the charger when unplugged.
Yes you can put on different size batteries at the same time. It is not recommended to leave your batteries on the charger when unplugged.
always
Yes, it happened to me too, when the batteries are charged, unplug the charger. I returned the charger for full credit, and purchased another.
Wrong chemistry. Since the newer ones are dual chemistry, they can handle both.
No, it cycles through each battery individually.
Manual does not list charge rate "per port" and from monitoring mine it appears to be charging one battery at a time and rotating thru each of the ports that have a battery plugged in. Mine works very well and after plugging in 6 batteries in the evening, all 6 are fully charged in the morning.
The charger charges only one battery at a time. When one battery is done charging, it switches to the next that needs charging. The input power is specified as 85 Watts. You can take that as a maximum.