Changing the auxiliary battery in a 2018 Jeep Compass can be confusing if you’ve never done it before. Many owners don’t even realize their car has two batteries—one main and one auxiliary. The auxiliary battery helps with start-stop systems, accessories, and sometimes electronic stability features. If your dashboard shows a battery warning or your stop-start system isn’t working, your auxiliary battery might be the problem. Replacing it yourself can save money, but you need to follow the right steps to keep your Compass running smoothly.
Why The Auxiliary Battery Matters
The auxiliary battery in your 2018 Jeep Compass is smaller than the main battery but just as important. It powers electronics when the engine stops at red lights and helps restart the engine quickly. If it fails, you might notice features like auto start-stop, radio memory, or USB charging ports stop working. Some drivers ignore the warning signs until the car develops electrical problems. Replacing the auxiliary battery before it fails completely can prevent bigger issues.
Tools And Parts You’ll Need
Before you start, gather these tools and materials:
- Replacement auxiliary battery (AGM type, Group Size 400 or compatible)
- 10mm wrench or socket
- Flat-head screwdriver
- Gloves and safety glasses
- Clean rag
Most auto parts stores can help you find the correct battery for your Compass. Always double-check the part number.
Step-by-step Guide To Change The Auxiliary Battery
Follow these steps to replace the auxiliary battery safely and correctly.
1. Turn Off The Car And Remove The Key
Make sure the car is off and the key is removed. Wait at least five minutes for electrical systems to shut down.
2. Open The Hood
Release the hood latch inside the car and prop the hood open securely.
3. Locate The Auxiliary Battery
In the 2018 Jeep Compass, the auxiliary battery is next to the main battery, often under a plastic cover near the fuse box. Remove the cover by unclipping or unscrewing it.
4. Disconnect The Negative Battery Terminal
Using your 10mm wrench, loosen and disconnect the negative terminal (black) on the main battery first. This prevents short circuits.
5. Disconnect The Positive Terminal
Loosen the positive terminal (red) and carefully move it aside.
6. Remove The Auxiliary Battery Clamp
There may be a small bracket or clamp holding the auxiliary battery. Use your wrench or screwdriver to remove it.
7. Take Out The Old Auxiliary Battery
Carefully lift the old battery out. Be gentle—don’t tip it or touch both terminals at once.
8. Clean The Battery Tray
Use a clean rag to wipe away dirt or corrosion. A clean tray helps the new battery sit properly.
9. Install The New Auxiliary Battery
Place the new battery into the tray. Make sure it’s facing the same way as the old one.
10. Secure The Battery Clamp
Reinstall the bracket or clamp to hold the battery in place.
11. Reconnect The Terminals
Connect the positive terminal first, then the negative terminal. Tighten both but don’t overtighten.
12. Replace The Battery Cover
Snap or screw the cover back over the batteries.
13. Start The Car And Test
Start your Jeep Compass. Watch for warning lights and test the start-stop system. If everything works, you’re done!
Comparison: Main Battery Vs Auxiliary Battery
Here’s a look at how the two batteries in your Compass compare.
| Feature | Main Battery | Auxiliary Battery |
|---|---|---|
| Purpose | Starts engine, powers systems | Supports electronics, start-stop |
| Size | Larger (Group 48) | Smaller (Group 400) |
| Location | Engine bay (front) | Near main battery |
| Lifespan | 3-5 years | 2-4 years |
Signs Your Auxiliary Battery Needs Changing
Pay attention to these warning signs:
- Auto start-stop not working
- Electrical accessories failing
- Unusual warning lights
- Trouble restarting after a stop
If you see any of these, test the battery soon.
Common Mistakes To Avoid
Many first-timers make these errors:
- Forgetting to disconnect the main battery’s negative terminal first. This can cause sparks or damage.
- Using the wrong battery type. The auxiliary battery must be AGM (Absorbent Glass Mat) to handle frequent charging.
- Not securing the battery properly. Loose batteries can move and get damaged.
- Not resetting warning lights. Sometimes, you need to drive a few miles or use a code reader to clear errors.
Table: Average Cost Of Battery Replacement
See how the auxiliary battery compares in price to the main battery.
| Battery Type | Average Price (USD) | Labor Cost (USD) |
|---|---|---|
| Main Battery | $120-$180 | $30-$50 |
| Auxiliary Battery | $60-$110 | $20-$40 |
Replacing the auxiliary battery yourself can save you up to $50 in labor fees.
Tips For A Smooth Replacement
- Always wear gloves and eye protection.
- Take a photo before removing anything—helps with reassembly.
- Dispose of the old battery at a recycling center.
- Double-check polarity when connecting terminals.
- Drive for at least 15 minutes after replacement to let systems reset.
What Not To Overlook
Many owners forget that the auxiliary battery is not charged by a standard battery charger. If you try to “jump” a dead auxiliary battery, it won’t fix the problem. Also, the auxiliary battery supports the start-stop system only if it’s healthy—if your Compass disables this feature, check the battery before visiting a mechanic.
For more technical details about the Jeep Compass electrical system, visit the official Jeep website.
Frequently Asked Questions
How Long Does The Auxiliary Battery Last In A 2018 Jeep Compass?
The auxiliary battery usually lasts 2 to 4 years. If you use a lot of electronics or drive short trips often, it may wear out faster.
Can I Drive My Jeep Compass With A Dead Auxiliary Battery?
You can drive, but systems like start-stop, some accessories, and even remote start might not work correctly. It’s best to replace the battery soon.
Do I Need To Program The Car After Replacing The Auxiliary Battery?
Usually, no programming is needed. The car’s computer should recognize the new battery after you drive for a short time. If warning lights stay on, a scan tool may be required.
What Happens If I Install The Wrong Battery Type?
Using a non-AGM or wrong-sized battery can cause poor performance, system errors, or battery failure. Always use the recommended AGM Group 400 auxiliary battery.
Where Can I Recycle My Old Auxiliary Battery?
Most auto parts stores accept old batteries for recycling. Never throw it in the trash, as it contains hazardous materials.
Replacing the auxiliary battery in your 2018 Jeep Compass is a smart way to keep your car reliable and avoid unexpected problems. With the right tools and careful steps, you can do it yourself and save money. If you ever feel unsure, ask a professional mechanic for help.
