There are a few variables that I think explain why LF batteries are not taken into account.
If the sail is charging the main battery then you have to find another way to charge the LF battery if you want to charge it at the same time. For a warship that can carry fuel or a jumpship that has a dropship on it's collars to borrow fuel from this isn't too much of a problem. Since these are variables that are likely to be outside a player's control it makes sense not to include any time savings.
As for recharge stations they actually don't decrease charging speed that much. I know a lot of players have this misconception that a ship can show up, pay a fee, and be recharged in a rather short amount of time but that has never been the case with them. Where they are most useful is in systems with dim stars where charging from the sail will take longer but even then you're probably only going to save a day and a half with no quick charge roll. If you want to quick charge, especially with the -2 from direct cable connections modifier, then you could get much more substantial time savings provided you make your roll.