This is the second time I am asking this question. The first time DJI admin reponded with an explanation for the Spark battery.
So, I am trying again to get an accurate answer.

Please tell me which battery type is used in the Remote Controller:
NiMH
NiCd
LiPo
Li-ion
Other (please specify)

It is a single lipo cell.
The 2940mAh battery specification together with the rc using 950mA@3.7V also hint at this.

Hi, thanks for the inquiry, we will forward this to our engineers for clarification and also provide accurate information. Your patience is highly appreciated.

If it is a LiPo should the RC be left on until its charge has dropped to 50% (2 lights) if it will not be used for a while (>3 days)?

From what I've heard it's not like the Intelligent Battery for the Spark...you can leave it fully charged, or not...your choice.

The spark batteries themselves are able to do a partial discharge for storage.
The rc battery is not. When it is fully charged, aging goes faster.

I always charge mine on the day I’m going to fly. Afterwards I leave it partially charged.
Just as I do with the spark batteries.

If a charge has become very low, I charge for about 15 minutes before storage.
And check the levels at least every month.