Lexus IS Battery: Specs, Fitment & Common Faults
A genuinely useful piece of context: if you own the IS300h hybrid specifically, the 12V battery genuinely can't be jump-started conventionally — it needs trickle charging, or the hybrid system's circuits risk damage.
Illustration for editorial purposes
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OEM Part Number: 28800-AZC35
| IS300h, current genuine reference (shared with RC300h) | Lexus OEM: 28800-AZC35 — S46B24L, 45Ah (also cross-referenced as 28800-YZZQX, 28800-YZZA1) |
|---|---|
| Alternative genuine reference (Panasonic-made) | Lexus OEM: 28800-36080 — S46B24L, 49Ah, 325A |
| Important | Even with the vehicle off and locked, the alarm and electrical system stay connected to this battery and will drain it over time if the car sits unused — worth knowing if diagnosing an unexplained flat battery. |
Lexus IS Battery: The Part Everyone Blames First, Not Always Correctly
When a Lexus IS won't start, the battery is the first suspect more often than anything else, and it's right often enough that checking it first is a reasonable move. It isn't always the actual cause though, which is worth knowing before paying for a replacement that solves nothing.
Lexus IS Battery: What It Does
Starting the engine and running electrical systems whenever the engine isn't turning — that's the Lexus IS's 12V battery job. If it has stop-start, it works much harder than older designs, since the engine cuts out and restarts constantly, which is exactly why it needs a specific AGM or EFB battery rather than a standard one.
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A Genuinely Useful Piece of Context Worth Knowing — Lexus IS Battery
If you own the IS300h hybrid variant specifically, this is genuinely important: because it's a hybrid, the small 12V auxiliary battery genuinely cannot be jump-started in the conventional way. Instead, it needs to be trickle charged, since attempting a standard jump-start risks genuine damage to the hybrid system's circuits. This doesn't apply to the conventionally-engined IS variants, worth confirming which specific version you have before assuming this limitation applies.
It's also genuinely worth knowing that on hybrid variants of related Lexus models, the average price for a 12V battery replacement has been documented at around £247, worth using as a rough benchmark.
Lexus IS Battery: Warning Signs, DIY Difficulty & Aftermarket Advice
These are the same regardless of make or model — see our full Battery Guide for warning signs to watch for, confirming fitment against your VIN, and matching the right technology (standard, EFB, AGM) when buying aftermarket.
More Lexus Battery
The same part, covered across other Lexus models.