Mercedes-Benz SLK 300 R172 Auxiliary Battery Replacement

In this guide, you will find instructions on how to replace the auxiliary battery on a Mercedes-Benz R172. The auxiliary battery may also be referred to as the G1/13 and its main function is as a backup to operate the ECO start/stop function of the vehicle.

The auxiliary battery on the R172 is located behind the driver's seat. 

What you will need

• Auxiliary Battery Specs: 12V 12Ah 170A
  • OEM: A2115410001
  • Alternative: YTX14 BS Battery 
• Metric Socket Set
  • 10mm socket
  • Ratchet Wrench 
• Dashboard Trim Removal 
  • Or Flathead screwdriver 
• Electrical Tape

Instructions

1. Open the river's door then use the seat switch to move the driver seat forward and also tilt the back reset forward. 
2. Ensure the ignition is turned off. If the vehicle is equipped with Start/Stop store the key away from the vehicle. 
3. Remove the luggage net located behind the driver's seat. It is held in place with 4 clips.  Just need to push the metal frame to release it from the clips. 

    

4. Next, you need to lift up the rectangular-shaped carpet. This will expose the access cover for the auxiliary battery behind it. 

    

5. Remove the two nuts on each end of the bracket. 
6. Remove the bracket to expose the auxiliary battery.  

    

7. Disconnect the negative terminal using a 10mm socket. 
8. Disconnect the positive terminal using a 10mm socket. 
9. Use electric tape to insulate the positive terminal. This will prevent any short between positive and frame. 
10. Disconnect the vent hose on the side of the auxiliary battery. 

     

11. Remove the auxiliary battery by pulling it forward. 
12. Install the new battery. 
13. Connect the vent hose. If the replacement battery is AGM it won't have a vent connection. This is ok. 
14. Connect the positive terminal first. 
15. Connect the negative terminal last. 
16. Reinstall the battery cover, lower the carpet cover, and install the cargo net.