Sorry if this has been asked before, but I was not able to find it anywhere.  

Is it safe/smart to keep your Spark batteries on the Charging Base station (NOT ON THE DRONE) until your ready to use them again?  I don't plan on keeping the controller plugged in, and I don't see me not flying my drone for more than a day or two at a time.

Personally - I give them a full charge and then take them off.  At ten days they will auto discharge down to 60% which is the best for this type of battery.  Then, if I think I'm going to fly, or once per month, I put them back on the charger.  This seems to be the most recommended practice.

Can't tell about leaving them on the charger, since I take them off after charging.

Just like to add one thing:
If I don't  know if I (wanna) use them in the next days, I recharge them after usage just to 2 1/2 LEDs.
In case I wanna fly, this way it needs about 45-5x minutes to refill 3 with the bay. Or one in just ~20 minutes, in case it is "urgent"

I changed that behavior when I had some batts a couple of times  auto discharged (no time, weather, ...).
This way, I don't stress them with 100% for to long.
Also I found out (tested), with 2 "equal" batteries, that a fresh charge (I count a day before  as "fresh") gets you more flight time, over one that's 1 week stored.
About 1 minute, which ist almost 10%, isn't it?

Hi, thank you for bringing this query for us. We do not recommend leaving the batteries of your DJI Spark in the battery charging hub when you are planning not to use it for a couple of days. You may refer to the DJI's battery safety guidelines for the DJI Spark for you to store your battery properly. Please don't hesitate to reach us if you have any inquiries or concern. Thank you for your continued support!

https://www.dji.com/spark/info#downloads

Thanks everyone, first time drone owner here and I didn't want to ruin my batteries already LOL