modifications > Grimmspeed Battery Kit

Why did you put a Grimmspeed Battery Kit on your RS?

The factory Focus RS battery is very large in size and heavy as well. My tuner (Adam with Tune+) turned off the auto start/stop function with the tune I uploaded to my Accessport, so I don't need as large of a battery. I waited for months and Grimmspeed finally released their lightweight battery kit for the RS. The only downside to a battery this small is that it needs to be maintained if you don't drive your vehicle. I use a battery maintainer in the garage.

The main benefit for doing this? Dropping 31 lb of weight off the front of my RS!

Date Completed:



- Grimmspeed Battery Kit (including battery)
- Terminal Protector Kit (O'Reilly's)
- Loctite for SAE battery terminals
- Sweet Tea (optional)
- Permatex Anti-Seize Lubricant (for hardware)


- 1/4" drive ratchet, handful of extensions, a few short sockets (10mm, 12mm)
- 10mm combination wrench to remove negative terminal from factory RS battery
- 13mm combination wrench for the Grimmspeed bottom tray bolt on driver side
- Trim removal tool or needlenose pliers to remove airbox sensor harness from airbox
- Allen (hex) wrenches (4mm, 5mm) for Grimmspeed bottom tray bolts
- Scissors or razor to cut (+) battery terminal protector
- Roku shop TV with Pandora blaring (optional)
*A friend for moral support is always optional.


1. Install takes about 2 hours or so. I took my time because of taking pictures for this website.
2. I used 12 pictures (#9 to #20) from the downpipe install. The only thing outdated in those pictures is the missing UPR oil cap breather.
3. I recommend doing this swap on a somewhat cold engine. Otherwise you might get toasty a few times in cramp quarters near hot engine spots.
4. There are no instructions other than the Blake's Garage video here. If it doesn't fit don't force it. Try not to zap yourself with the battery leads.
5. Only (1) wiring plug needs to be disconnected for this swap. Airbox sensor.
6. Make sure to reinstall the (2) wiring harness leads on the lower front of the battery (plastic wall).
7. Leftover parts = Odyssey battery terminal hardware.
8. Easily reversible back to stock for gaining 31 lb. But that would be crazy talk.
9. Make sure to re-use Odyssey (+) terminal cap on factory RS battery to prevent sparks in storage.
10. Weights:
       OE battery + box + bolts = 47.4 lb
       Grimmspeed battery + brackets + bolts = 16.4 lb
       Total weight removed = 31.0 lb

Optional positive battery terminal protection.