Side-post on most XJs. Corrosion under the terminal block is the #1 cause of starting issues. Annual load test prevents winter strandings.
XJ batteries are top-post on 1984-1990 and most 1991+, though side-post examples exist. The negative cable on the 4.0L is bolted to the head with a 10mm under the intake - this connection corrodes and causes a wide range of mystery electrical problems including dim dash lights, slow cranking, and random no-start. Disconnect both terminals, remove green corrosion with a wire brush, apply dielectric grease or terminal protectant spray, retorque to spec (about 7-10 ft-lb). For load testing, most auto parts stores will load test for free; a 65-amp draw should hold the battery above 9.6 V for 15 seconds at 70 F. A failed load test or specific gravity under 1.225 means replacement. Group 34 or Group 26 fits the stock tray; Group 34/78 dual-post is a popular upgrade for adding aux wiring posts.
| Part | Vendor | Est. price |
|---|---|---|
| Battery (Group 34) | Interstate/Costco | ~$130 |
| Battery terminal protectant | auto parts | ~$5 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.