The chargers are mentioned in at least 3 different places on the hotel website:
https://www.eden-spiez.ch/en/sustainability
Four charging stations for electric cars in our parking garage
https://www.eden-spiez.ch/en/contact
Our modern and large parking garage offers plenty of space for your car in addition to 4 charging stations. We kindly ask you to let us know in advance if you need a garage space.
(CHF 12 per car/night without electricity, CHF 5 flat rate per day for e-charging).
https://www.eden-spiez.ch/en/getting-there
If you come by car, you will find parking spaces in our bright and clearly arranged indoor car park - 4 of them with charging stations for electric vehicles. Parking spaces are subject to a charge and it is not possible to reserve a parking space.
For the use of our e-charging station we charge a general fee of CHF 5.00. This price is per day and vehicle and is independent of the charging time. Please register at our reception. (A cable is not available!)
On Chargemap there's a comment from December 2019 that says the charge is 40ct/kWh. This must have changed since then.
On Chargemap as well there's a picture inside the underground garage but we don't see the stations.
I walked through Spiez today, we don't see anything from outside. To enter the parking garage it seems like you're supposed to drive through the paved courtyard and at the end there's an illuminated sign with the number of free spots in the underground parking. Next to the ramp there's a sign saying for customers only. They also have outside parking spots but I didn't see any charging station there.