5420 Charging

Hi, I have a Dell 5420 which I have started using with a Startech dock - this one - https://www.startech.com/en-gb/universal-laptop-docking-stations/dk30ch2dppdu

It can charge the laptop, meaning i have only one USBC cable to connect to the laptop when i am at the desk, and that gives me internet, video out for desktop screen, USB, audio etc etc, and also charges the laptop. 

This frees up my Dell charger to keep at home for when I take it back. 

It seems to be working fine but it suddenly occurred to me maybe this is not good for the laptop's battery. Does anyone know for sure? In my understanding of batteries, it shouldn't do any harm as even if the wattage is a bit lower, that just means a slower charge which can often mean its actually better for the battery's longevitty. 

If anyone knows for sure, I'd be grateful to get confirmation that it won't do any harm. Thanks