Perhaps the war crime that the French are complaining about is the killing of the French prisoners at the end of the battle? Much money could be made by the rank and file by capturing a noble who would then pay a ransome for his safe return home - a man of high rank could set a squire up for life, and as for a King's Ransome..... Many French nobles had surrendered during the fighting (nothing new there then), but when there was the threat of a French attack late in the day - an assault on the baggage train - King Henry ordered all the prisoners killed to avoid their release. Mind you, this probably upset his own troops more than the victims because it cost them much in lost allowances!
How familiar it all sounds......
PS. I don't hear the French complaining about the murder of the Hugenouts during C16.