Because there haven't been any made without a float since about the early 90s giving this question a good guess. I can't recall the exact year when manufacturers switched from the old transformers to "switch mode" design, but it was about that time. Put a meter on your battery and you will see it floating a charged battery at about 13.3-13.5 volts. Batteries with these converters will still lose water over time, but nothing like in the past. If you have a meter and know how to read amps, put your meter in series with the lead on the battery and check the amp input.
However, again, continuously staying plugged into the shoreline with the converter operative is not necessary nor recommended by manufacturers. It does keep the battery charged, but converter life is limited and staying plugged in continuously you are using converter life when the camper is sitting. Just plug in every month or so for a day and your batteries should be fine and water loss will be minimal.
Those with solar may have the best charging source although given the cost of solar it can be a pricey way to extend battery life, if that were the only goal.