In the past, I bought some 5-volt / 3.3-volt level shifters, and was astonished how far off the actual voltages are, and yet they are considered "good", and they work.
Later, I bought some audio breakouts, and was again surprised that the 3.3-volt source they supply (from the 5-volt they run on) actually produces 4.1-volts instead. (In that case, I added an external 3.3-volt regulator to get things right.)
Now I'm using the following circuit to charge the internal clock battery, and once again, voltages just don't match what literature says they are going to be.
The source voltage (supplied by the laptop USB) is actually 5.17 volts, not 5.0. The output from the regulator is actually 3.41 volts, not 3.3. And the voltage between diode and resistor is currently 3.25, instead of 3.1, which will undoubtedly rise as current slows down from the battery reaching full charge.
I would think these differences too little to matter, if it were not for the literature on this specific battery stating:
(1) 3.1 volts is the accepted standard charging voltage. (2) The charging voltage may be between 2.8 and 3.2 volts. [3) Exceeding this limit will cause the battery resistance to rise, and may cause battery deterioration.
Actually, the clock came with an internal charger I could turn on, but the built-in charger is a resistor in series with a diode connected to the 5-volt source; clearly a "trickle-charger" by definition. So I didn't use it because the battery's literature states:
Under no circumstances should trickle charging, which is used for nickel-cadmium batteries, be used. Ignoring this precaution will cause the battery voltage to rise to about 5V, resulting in a deterioration of performance.
(What were the manufacturers of the clock breakout thinking?)
I feel like no one up there at these various manufacturing companies knows what's real, and they all just spout personal theories, claiming it to be the gospel truth when it isn't.
Should I take anything they say seriously? How can I be sure I'm not selling a product with batteries headed for "China Syndrome", due to my following their instructions?