Your analogy is right and you could have answered your own question with it too..
I'll give you another one.
When series-ing batteries, the ONLY thing that changes is voltage.
So by saying that.. let's look at a 12v battery.
a 12v battery has 6 cells in series.
That means that each cell can do the same current value.
that means, if you take a Odyssey PC2150, EACH CELL can output 2,150A for 5 sec, 5000A for 0.1sec, etc...
So, when looking for 2v cells, make sure you match similar ratings to your existing batteries.
Also, i would only advise doing this for competition only. If for daily, i'd HIGHLY recommend putting a solenoid in between EVERY 12v to 2v cell combination you have to prevent your batts and cells from killing each other in the long run.