Battery cases are they bad long term?

[tshirttan408]

Hi guys, so I'm considering getting one of those battery case thingys but wanted to ask if people think they have a negative effect on your battery long term?

 

[Tim1954]

They are just another charger. I use one permanently on my S7 (which is my second/spare).
My main driver is the S8 and I have wireless charging pad in my car, otherwise I'd have one on it too...