It is physically the same size and shape, but it has a lower capacity (9Ah as opposed to 16Ah) and due to decreased number of simpler cells it can be charged on an unmodified lead acid charger (whereas the L16 requires an up to date lead acid charger with a replacement chip for the li-ion charging profile, or of course the li-on charger).
I think a little bit more to it than that.
The charging voltage of LiIon cells must not exceed 4.2V. Also, lead acid chargers vary quite a lot. There is original type whereby a voltage of 5V was applied with a resistance used to keep the current down to reasonable bounds. Then there is the later electronic type which cuts off the charge current completely when the battery is fully charged.
A bit off topic, but your modern car works the same way, how often do you have to top the battery up these days?
In the old days charge would continue, albeit at a trickle, but sufficient to cause a small degree of gassing and the consequent loss of electolyte.
My avatar is a poor likeness.