Asking for a suggested power controller for a battery charger
Do you have the batteries disconnected? If not you are reading the charger output, not the battery voltage.
There is no charger connected, being accused of trickery? I see this is NOT the forum for me.
I'm out of here
@poundsand NOT trickery, just a common mistake.
Arduino says and I agree, in general, the const keyword is preferred for defining constants and should be used instead of #define
"Never wrestle with a pig....the pig loves it and you end up covered in mud..." anon
My experience hours are >75,000 and I stopped counting in 2004.
Major Languages - 360 Macro Assembler, Intel Assembler, PLI/1, Pascal, C plus numerous job control and scripting
I am certain Ron (@zander) was not accusing you of trickery, and he is correct in saying that having the charger connected is indeed a common mistake. Ron kindly answers a lot of queries, and a fair percentage of all the queries include the questioner making a mistake .. which we all do from time to time.
Li-ion batteries are not a 'single design fits all', but rather there are several variations, and their no-load voltage varies accordingly. Furthermore, some chargers may tend to charge to '100%' , whilst others may cut off before reaching '100%', to increase the life of the battery.
For comparison, I just checked a single 18650 cell from a headtorch I bought recently, and it registered 4.06V.
I don't claim my multimeter is particularly accurate, though it usually shows what I expect, so I think it is reasonable.
But obviously, if I had 4 such cells in series, then the voltage would be 4 * 4.06 = 16.24 V
So your reading of 16.42 V, give or take a reasonable meter margin, appears highly plausible, but may differ from other peoples' experience.
Best wishes, Dave