A 3 phase charger will charge your battery more effiently than a single phase.
That said, every battery has a battery amp hour rating, the charger should meet that rating, or at least w/in 10%. Example, a battery w/ a 750 amp hr, should have a charger w/ at least a 675 amp hr rating.
Now that said, a lower rated charger of 15% will still do the job but w/ less effiency. In practicality, it will take longer and may not reach the complete 80% (full charge), lowering the life of the battery.
Now that said, I have seen a small company using a forklift several times a week (1 or 2 hours operating time), w/ a smaller charger and got years of use out of the battery (w/ proper battery maintanance).
I'm sure some electrical engineer will argue the point, but I've got a EE as well, and found that real life practical experience will always out weigh calculations to the 5th decimal point.
Hope that helps you.