How does 4 times 2V give 12V of power?
It doesn't. It gives you 8V of power.
RLENT's L-16 are the 6-volt batteries.
The L16 is a BCI (Battery Council International) battery size, like the Group 27, Group 31, Golf Cart. The L16s are mostly designed for floor scrubbers, in the 6-volt configuration. For the 2-volt configuration, that's mostly for renewable energy installations, like wind or solar, off-the-grid type stuff. You usually see these in larger systems where 12 or 24 of them are connected in series for a 24-volt or 48-volt bank.
This link is for
Concord Lifeline Batteries, but it gives a good table of different battery sizes, capacities and other specs one can use for comparisons.