Now it’s getting to technical for me.
I’ve got 5400 mah 4s 14.8 volt batteries.
How far “extra” do you think is save to charge?
Have you been using the OEM charger that came with your Typhoon H? If so, then you have been charging your batteries to 16.8 V.
Look at the battery voltage display on the ST-16 when you first power on the aircraft. It will usually read 16.7 or 16.8 Volts. What voltage do you usually land at? Most try to be on the ground by 14.5V. The first low battery alarm will occur at 14.3V.
Post #17 by @Mrgs1 is on the mark. The TH battery is a 4S meaning there are four cells in series so their voltages add together. The nominal voltage of 3.7V times 4 gives 14.8V., and full charge of 4.2V gives you 16.8V.