Rapid charging of “energy cell” (e.g. lithium-cobalt) type Li-Ion batteries, say at 2C, 3C or higher, is well known to reduce battery lifespan.
On the other extreme, does charging at very low rates, say C/10 or C/20, have any effect on their lifespan?
For instance, I charge my portable devices such as phones and tablets using a 2.5 W charger. My thinking is that any extra time spent charging is time not spent discharging, which would contribute to extra cycles on the battery, as well as slightly reducing temperatures, since high temperatures are also known to be detrimental to battery lifespan. I also use limited-wattage-output power banks to (very slowly) charge my laptop battery while away from a power outlet.
While the effect on these variables may be minor, it should be beneficial or at most irrelevant. What I’m looking for are any references to detrimental effects from slow charging.