There is no quick way to safely charge batteries. Using the smart mode chargers will get a 50% charge state battery up to its 90% charge state in three hours charge time. To get to the 100% charge state it will take around 12 hours. Most batteries will perform almost at full performance at the 90% charge state but the down side is you only get so many 50% to 90% charge cycles before doing damage to the batteries. In my case I get by real good doing around 12-14 50%/90% charge cycle before I have to a full 100% charge cycle.
This is using the 14.4VDC-13.6VDC and the 13.2VDC charging voltages from a smart mode charger.
You can charge the batteries up quicker by using a higher DC CHARGE VOLTAGE but doing this may boil out your battery fluids by getting them real hot in the process. You also may have your battery blow up on you in rare cases..
The Industry now somewhat sticks to proven charge rates to keep your batteries working great and long lasting...
lots of good info on this on-line if you want to read up on how to safely charge your RV BATTERIES...
Roy Ken