I'm building a battery charger that can charge multiple batteries at a time, and I'm currently looking at Linear Tech's LTC4011 IC, but I think it can only change once battery at a time (a single battery containing up to 16 cells, as I understand it). Are there any ICs that can charge multiple batteries simultaneously yet separately? (Also, how might an IC such as the LTC4011 react to charging multiple batteries that are placed in series, "pretending" to be one big battery?) I imagine the chemical charging profile would be all messed up if the individual batteries aren't all at the same charge when plugged in)
From the LTC4011 datasheet:
Based on this, I think that the charger IC determines the average single-cell voltage input and uses that as a basis for how much current to charge with. So if you have a dead battery and a 100% battery connected in series, it would detect 50% voltage and charge at a normal rate, therefore damaging your fully charged battery.
Further it states in the datasheet at the bottom of page 22 that "charging parallel cells is not recommended". So it appears this IC was designed with only one battery pack in mind. If you are looking for something that will charge multiple batteries separately, you might have to use a multi-port charger from HobbyKing or something, those will typically run you > $50 USD based on what I have seen searching the website.
I have never seen such an IC. I do not think it exists. I believe that the chargers which have this functionality (independent charging of multiple cells) use a specialized microcontroller to monitor all the cells.
If you do this, you may also consider including temperature sensing, although this is not necessarily required. It would allow you the option of doing dT/dt charge termination.
It really is much better to charge each cell individually compared to charging in series pairs as many NiMH chargers do.
The charger shouldn't see a difference between multiple series cells regardless if they are individual cells or battery packs. NiMH batteries are just raw cells. As long as the voltage limits are observed it should work the same. A charger IC that can do a 9.6V battery could do 8 series cells, but can't do 9.