Well from what I understand on lithium 's (i have 2 on my current robot, rebuilding it) is that a 3.7v is fully charged at 4.2v so it charges at 4.2v. The 2S one is 7.4 but fully charged at 8.4. which is why the charger is at 8.4v, is that right?
Well. the 8.4 V can from the datasheet of the chip. the 844 model is setup at 8.4 V. The other chip number 841, 842, 843 are setup differently. ← To my understanding of the datasheet. Depend of the chip number you have access ← I thinking you trying to “hack it up” ← my guess , you are stuck for the charging voltage, but you can modify the charging rate ( 1 A, 2A 3 A ← what ever )
My opinion is : caution… you don’t want to “burn”, “blow up” or “damage” the battery being charge. I recommend to experiments and see what happen. I am just an hobbiest who went to DeVry in 1990’s , work as a tech for 3 years in the 1990’s and I try to re-kindle the passion I have with electronics. I am not familiar with this chip, but commun sense tell me : caution and experiments.