2019 Jeep Compass Auxiliary Battery: Complete Replacement and Troubleshooting Guide
The 2019 Jeep Compass uses a dual-battery system that confuses many owners. When your start-stop system fails or struggles to restart at stoplights, the auxiliary battery is often the culprit. This guide explains replacement, costs, and troubleshooting to save you $500 over dealership pricing.
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What Is the Auxiliary Battery in a 2019 Jeep Compass?
Your Compass has two batteries. The main battery handles engine cranking and high-power demands. The auxiliary battery supports the Electronic Start-Stop (ESS) system exclusively.
The auxiliary battery powers electronics when the engine shuts off at red lights—radio, climate controls, dashboard displays, and accessories. This keeps the main battery fully charged and ready to restart the engine instantly.
Both batteries connect through a parallel charging system controlled by an Intelligent Battery Sensor (IBS). This sensor monitors voltage, current, temperature, and charge state, directing the alternator to charge batteries based on real-time conditions.
The auxiliary battery specification is Group Size 400 (AUX14). It’s an AGM battery rated at 12 volts, 12-14 amp hours, and 200 cold cranking amps. Dimensions measure 5.9 x 3.4 x 5.7 inches.
Where Is the Auxiliary Battery Located?
The auxiliary battery sits in the engine compartment on the driver’s side. It mounts directly in front of the main battery, secured by a bracket with a 13mm nut. You’ll find it between the main battery and coolant reservoir.
Open the hood and locate the battery area. The larger battery is the main unit. The smaller battery in front is auxiliary.
The negative terminal faces the driver’s side. The positive terminal sits under the coolant bottle on the passenger side. Both use 10mm nuts for cable connections.
Common Symptoms of Auxiliary Battery Failure
Dashboard messages reading “Start/Stop Unavailable Service Stop/Start System” indicate failure. This appears when the IBS detects insufficient battery capacity.
Hard starting at stoplights signals problems. When the engine shuts off and struggles to restart, your auxiliary battery lacks charge. A weak auxiliary battery drains the main battery during restart attempts.
Overnight battery drain points to auxiliary issues. A failing auxiliary battery pulls current from the main battery even when parked. You’ll jump-start the Compass frequently despite a relatively new main battery.
The EVIC may show “Battery Charging” or “Start/Stop in Battery Protection Mode” messages. These confirm the IBS-recognized battery problems and disabled the start-stop system.
Sluggish cranking suggests both batteries need attention. The auxiliary battery fails first, then drains the main battery over time. By the time you notice starting problems, both batteries require replacement.
Why Both Batteries Should Be Replaced Together
Replace both batteries simultaneously or face repeated failures within months. The parallel charging system creates electrical interdependence.
Installing only a new main battery leaves the old auxiliary battery as a constant drain. The parallel connection allows the weak auxiliary battery to pull current continuously. Your new main battery fails within weeks or months.
Replacing only the auxiliary battery while keeping the old main battery causes problems. The aged main battery can’t properly charge the new auxiliary battery. The IBS recognizes voltage discrepancies and triggers warning messages.
Battery age mismatch confuses the IBS. When one battery is new, and one is old, the IBS can’t optimize charging for both. This causes undercharging or overcharging, reducing lifespan.
AGM batteries are damaged easily by incorrect charging. The IBS needs both batteries in similar condition to calculate proper charging voltages. Dealerships recommend simultaneous replacement to avoid paying labor twice.
Auxiliary Battery Replacement Cost Breakdown
Dealership pricing ranges from $700 to $900 for both batteries installed. This includes parts, labor, disposal fees, and overhead.
DIY replacement costs $400 to $450 for both batteries. Main batteries run $180 to $275. Auxiliary batteries cost $70 to $160. Major auto parts retailers carry both batteries.
Cost Comparison by Retailer:
- O’Reilly Auto Parts: $434 for both batteries
- AutoZone Duralast Platinum AUX14: $160
- Walmart auxiliary batteries: $70-90
Dealerships charge $200 to $400 for installation labor alone. Replacement takes 30 to 60 minutes for first-timers. Experienced DIYers complete the job in 15 to 20 minutes.
You’ll need 10mm and 13mm sockets, a socket wrench with extension, dielectric grease, and safety glasses. Some auto parts stores offer free installation with battery purchase. Call ahead to confirm availability.
Step-by-Step DIY Auxiliary Battery Replacement
Position the vehicle on level ground in a well-ventilated area. Gather tools before starting.
Safety Precautions
Turn off the ignition and remove the key fob. Ensure all electrical accessories are off. Remove metal jewelry to prevent short circuits. Wear safety glasses and gloves—AGM batteries contain sulfuric acid.
Remove the Intelligent Battery Sensor
Press the release tab on the IBS connector and pull straight up. The IBS is the black module on the negative terminal between the main battery and fuse box. Move it aside but leave it attached to the cable.
Disconnect Battery Terminals
Start with the main battery negative terminal. Use a 10mm wrench to loosen the nut. Lift the cable off and position it away from the battery.
Remove the auxiliary battery negative terminal next. Loosen the 10mm nut and position the cable away.
Disconnect the main battery’s positive terminal. Remove the red plastic cover if present. Loosen the 10mm nut and lift off the cable carefully.
Finally, disconnect the auxiliary battery positive terminal under the coolant reservoir. Move the coolant bottle slightly for access.
Remove and Replace the Auxiliary Battery
Locate the hold-down bracket secured with a 13mm nut near the washer fluid reservoir. Use a socket wrench with a 12-inch extension. Remove the nut and lift off the bracket.
Lift the auxiliary battery straight up. It weighs approximately 10 pounds. Angle carefully to avoid damaging coolant hoses.
Transfer the threaded terminal inserts from your old battery to the new one. Use a 10mm wrench. The positive insert goes on the left terminal, negative on the right. Hand-tighten first, then snugly tighten with a wrench.
Lower the new auxiliary battery into position. Align the hold-down bracket slots correctly. Install the bracket and tighten the 13mm nut until secure.
Replace the Main Battery
Remove the main battery hold-down bracket (10mm or 13mm fastener). Lift out the old battery—it weighs 35 to 45 pounds.
Install the new main battery with the positive terminal toward the front. Secure with the hold-down bracket.
Reconnect Terminals and Test
Connect terminals in reverse order. Start with auxiliary battery positive, then main battery positive, auxiliary negative, and main negative last. Tighten all 10mm nuts securely.
Reinstall the IBS on the main battery negative terminal. Push the electrical connector until it clicks. The release tab should face upward.
Start the vehicle and verify operation. The dashboard should display 13.5 to 14.5 volts while running. Let the engine run 5 to 10 minutes for IBS initialization.
Auxiliary Battery Specifications and Replacement Options
Group Size 400 (AUX14) is the only correct specification. Incorrect sizes cause improper fit, charging problems, and electrical damage.
AGM technology is mandatory. The Compass charging system calibrates specifically for AGM batteries. Standard flooded batteries damage from the higher voltages AGM batteries require. Never substitute a flooded battery.
CCA ratings range from 200 to 250 CCA. Higher CCA provides better cold-weather performance. Premium batteries like Optima, Odyssey, or Interstate often exceed 200 CCA.
Amp-hour capacity affects how long the battery powers accessories with the engine off. Standard auxiliary batteries provide 12 to 14 Ah—adequate for the typical 15 to 30 seconds at stoplights.
Terminal configuration must match original equipment. The auxiliary battery uses a positive left, negative right arrangement. Some aftermarket batteries ship with terminal hardware; others require you to transfer it.
Troubleshooting After Battery Replacement
Dashboard warnings sometimes persist after replacement. The IBS stores historical data that takes several drive cycles to clear. Most warnings disappear after three to five ignition cycles totaling 50 to 100 miles.
The start-stop system disables when voltage drops below 12.4 volts, outside temperature falls below 32°F, the hood is open, or HVAC demands high power.
New batteries require initial charging before reaching full capacity. Allow 50 to 100 miles of normal driving. Voltage should stabilize at 12.6 to 12.8 volts when off, 13.5 to 14.5 volts when running.
Most Compass models relearn IBS parameters automatically during normal driving. If problems persist beyond one week, visit a dealership for IBS reprogramming.
Apply dielectric grease to both terminals after installation. This prevents corrosion from moisture. Reapply every six months during maintenance checks.
Alternative Solutions and Considerations
Some owners remove or bypass the auxiliary battery entirely. This eliminates the start-stop system permanently but may trigger warning lights. Jeep doesn’t recommend this modification.
The dashboard button turns off the system manually at the end of each drive. Third-party start-stop eliminators automatically disable the system every ignition cycle for $50 to $100.
Unplugging the IBS disables start-stop but causes other problems. The IBS controls the alternator charging strategy. Without it, charging becomes less efficient, and batteries may overcharge or undercharge.
Battery warranty coverage varies. Mopar batteries include a 2-year unlimited-mile warranty. Aftermarket premium batteries often provide 3 to 4-year warranties. Original equipment batteries receive 3-year/36,000-mile coverage.
Frequently Asked Questions
Can I drive without the auxiliary battery?
Yes, but the start-stop system won’t function and you’ll see dashboard warnings. However, a failing auxiliary battery left installed drains the main battery and causes starting problems.
How long do auxiliary batteries last?
Auxiliary batteries last 2 to 3 years, shorter than main batteries. Frequent charging cycles from start-stop operation create more stress. Climate extremes reduce lifespan further.
What happens if I replace only the main battery?
The old auxiliary battery drains your new main battery within weeks or months. The parallel connection allows continuous current drain. You’ll experience starting problems and shortened main battery life.
Why does my auxiliary battery keep failing?
Frequent short trips prevent full recharging. Extreme temperatures damage internals. Manufacturing defects occasionally cause premature failure. Consider disabling start-stop to reduce battery stress.
Do I need special tools for replacement?
No. A 10mm socket, 13mm socket, and a socket wrench with an extension handle are all fasteners. Battery terminal cleaning tools and dielectric grease improve results but aren’t required.
Should I disconnect the negative terminal first?
Always disconnect the negative terminals before the positive on both batteries. This prevents short circuits if your wrench touches metal while removing the positive terminal. Reconnect in reverse: positive first, then negative.
Can AutoZone or O’Reilly replace my batteries?
Many locations offer free installation with battery purchase. Call ahead to confirm your local store provides this service. Some stores lack staff or equipment for dual-battery installations.
Will new batteries reset my radio presets?
Yes. Disconnecting batteries erases radio presets, clock settings, and some driver preferences. Write down your stations before starting. The Jeep relearns driving patterns over the next few days.
Is the auxiliary battery covered under warranty?
The original auxiliary battery is covered under Jeep’s 3-year/36,000-mile basic warranty. Mopar replacement batteries carry a 2-year unlimited-mile warranty. Aftermarket batteries include manufacturer warranties ranging from 1 to 4 years.
