One thing I have noticed on both bikes is that the charge rate is a few tenths of a volt higher in cold weather.
Charging a battery involves chemical reactions. The speed of these chemical reactions increase as the temperature rises, similarly the reactions become slower as the temperature is decreased. Lots of regulators have built in temperature compensation. They increase the voltage a few tenths during cold conditions to speed up the chemical reactions thus maintaining a good charging rate. At higher temperature where the charging reactions are faster the voltage regular lowers the charging voltage slightly to prevent overcharging and gassing.
A typical temperature compensation graph:
https://autoelectricalsystems.wordp...in-built-safety-and-temperature-compensation/
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