It stands to reason that lowering the wattage at which you charge your phone will be better for the battery by limiting the heat generated while charging.
“A battery warms up as it charges, which can reduce its lifespan. To reduce the effect of heat and prevent overheating, iPhone gradually reduces the charging current as the battery approaches full charge.”
Charge and maintain your iPhone battery - Apple Support
Maybe the benefit is not noticeable within the first year or so, but I would imagine this small change would have a greater effect over 1000+ charging cycles. Apple claims the battery in 15th gen phones should still have 80% health after 1000 charging cycles. This ends up being about 3 years of one charge a day… right when they want you to upgrade?
@mrleaw have you found a charging set up that works at 5W?