12V battery: test, jump-start or replace

Symptoms

The fix, step by step

1. The battery sits under the engine compartment cover: push the tab in, pull the lock release, lift the cover, then pull it forward.
2. To jump-start, open the positive terminal cover, remove the engine cover, and connect to the positive terminal and the metal ground point the manual shows (not the negative terminal).
3. Run the donor vehicle for about five minutes before you try to start.
4. To replace, turn the engine switch off, disconnect the negative terminal first, and fit a battery with the same LN4 case size, at least 80 Ah (20-hour rate) and at least 689 CCA.
5. The manual warns that a battery of a different size can't be secured properly, and an unsuitable one may not restart the engine.
6. Afterwards, re-initialize the power back door, and the moonroof and power running boards if fitted, plus the power windows if they act up.
7. The engine may not start on the first try after reconnection.
8. If you're planning a dual-battery setup, a GX 550 owner on IH8MUD says there's practically no room under the hood with the twin turbos, intakes and intercooler, so he put a lithium battery and a DC-DC charger behind the second row.

Tools & part numbers

• Socket set
• battery tester or multimeter (12.3 V or higher with the headlights test in the manual)
• jumper cables
• terminal brush. The smart key uses a CR2032, which the schedule replaces at 30,000 miles. Lexus recommends a dealer do it.

Where to buy the parts

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