The formula is simple.
Say you have a 1200mah battery, and a charger that puts out 300mah, it would take about 4 hours to charge that 1200 mah battery. 1200 divided by 300.So in your case you if you had 1600mah battery and a 900mah charger, it would take 1.7 hours to charge the battery.
If youve been cranking juice into a battery for since 11am till now, and the battery is fairly hot. There is a good chance the battery is damaged.
"Its only a little bit on fire"