There are two issues you need to resolve. One is the voltage, the other is the battery shape.
In terms of voltage, the original camera uses 1.35v, but many used cameras in the market have been converted to 1.55v. I have no way to tell whether your camera has been converted, but you can try the 1.55v Alkaline battery to see if the light meter is correct (use any other camera's light meter for reference). If your light meter tends to off by a couple of stops, then your light meter is not converted, you will need 1.35v battery.
Now, about the battery shape. You will need one of the following adapters, depends on the voltage of your light meter.
If your light meter is converted (to the 1.55v), congratulation, you will need this:
https://www.ebay.com/itm/1pc-PX625-Film-Camera-Battery-Adapter-for-ROLLEI-35-OM1-QL17/362918693948?hash=item547fa3cc3c:g:xvQAAOSwXzBeS5B0You will use this to take Li-On battery type "386" or the equivalent (it has mane alias name).
(warning: avoid this
https://www.ebay.com/itm/1-35V-MR-9-PX625-MRB625-Adapter-Battery-For-Film-Camera-Light-Meter-MADE-IN-UK/173228970297?hash=item2855405139:g:yGIAAOSwHU9eIPrDThis is the same as the above, but much more expensive, it may be unpurposed give you an impression it has voltage conversion).
If your light meter is not converted (needs 1.35v battery), you will need this:
https://www.ebay.com/itm/KANTO-Mercury-Battery-Adapter-MR-9-H-D-Voltage-Non-voltage-conversion-J0180/402487219437?epid=8007658362&hash=item5db61b94ed:g:1BgAAOSwt4xfgt5mThis may look like the first I recommended (see one above) but it has built-in voltage converted. It is expensive, but you do not have other choice as far as I know.
With this, you will need the same Li-On 386 battery (1.55v), but your camera will get the 1.35v out of the converted.
One more note:
if you are still considering Rollei 35S or 35SE, get 35SE. Same applies to 35/35T vs 35TE. There are many nonsense web discussions that recommend 35S over 35SE. The argument says the 35S needle type light meter is easy to view, can tell you how far your exposure setting it is from the right value, and you can view the meter without see through the view finder,..etc..etc. Here is my comment, use it with yr discretions:
1. The most important factor to me is the replacement of battery. The 35SE type battery compartment is accessible from out of there film compartment (on the top of the camera) while the 35S type is inside of the film compartment. If you are in the middle of a film, you can not change the battery if it is 35S, but you can with 35SE.
2. With the needle type, you will have to move you eye out of the view finder to judge the exposure. This is against the common tend of all modern light meter.
3. With the single LED indicator it is true you may not tell if you are under expose or over expose, you'll have to turn the exposure to wonder around to find it. (Big deal!) This is where the needle type wins.
4. The needle type light meter is far more fragile than the LED type against the physical impact.