Full force battle has 3 irritating features, the first being that it can take your precious resources when you do not win it on time, the second it has 22 hrs of timing instead of 24 hrs making it hard to predict the time it appears and lastly, it can be hardly predictable of the results (Gamevil always has a way of trolling players). However the only good thing that comes out of all this trouble are the red medals which are extremly precious (can't be bought with crowns) and very useful.
Currently at the moment there are 2 'time effecient' ways of doing ffb, if you follow this method u will find yourself completing it every single time when it appears with ease, but do take note that that this strategy requires you to be able to produce sufficient resources in time else you will start losing resources instead of gaining, you have been warned.
{ Normal strategy for most players }
Deploy x 64 of the "highest lvl unit" of the enemy units
Loss: 4 units
Time to replenish unit losses for next ffb:
4 hrs for lvl 5
6 hrs 24 mins for lvl 6
{ Special strategy for players who has everything else red and yellow stars (for high end players only) }
Split the deployment in 2 waves, prepare one set of 9 non star lvl 6s
Deploy x 9 lvl 5 units for first wave
Deploy x 9 lvl 6 units for second wave
Loss: 9 lvl 5 units & 1 lvl 6 units
Time to replenish unit losses for next ffb: 9 hrs & 12 mins
This will work 100% of the time, you just need to keep up with the resource reproduction, please also take note also that no matter what you do, you can never break past the minimum limit of 3 unit losses in ffb