If you have a "HI/LO" charge rate switch on your battery charger and the battery is well and truly flat, start if off on the "LO" setting for a few hours until it starts drawing some current (assuming you have an ammeter on your charger) and then switch it onto "HI". Be prepared to switch it back quickly though as the extra voltage from the charger may then push the charge rate off the limit of the charger.
Once it's had a few hours on the higher rate, switch it back to "LO" to give it an "equalising" charge, preferably overnight.
A rough rule of thumb if you're using a constant current charger would be about 4A on that battery. The approximate formula is battery capacity in A/h divided by 20 which gives about a 20 hour charge. In your case, 78 A/h divided by 20 is a gnats whisker under 4A.
Hope that's helpful for you.
