Toyota Yaris Battery: Specs, Fitment & Common Faults

On the Yaris Hybrid, Toyota's own dealer test may not let the battery stabilise before checking it, potentially masking a genuine problem.

Illustration for editorial purposes

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OEM Part Number: 28800-AZC33

Accuracy note: the Yaris Hybrid uses a small, separate 12V auxiliary battery, not the high-voltage hybrid drive battery — confirm which one you actually need before ordering, since they're very different components at very different price points.

Yaris Hybrid, 12V auxiliary (2011-2014, S34B20R)	Toyota OEM: 28800-AZC33 — 35Ah, AGM
Yaris Hybrid, 12V auxiliary (2013-2018, S34B20L)	Toyota OEM: 28800-YZZRD — 35Ah, AGM
Standard petrol Yaris (Mk4), Start/Stop	Type 027, EFB, approximately 60Ah, 640A (EN)
Note	There are left-hand and right-hand terminal versions of the hybrid auxiliary battery depending on market — confirm the correct terminal orientation for a UK car before ordering.

A Genuinely Significant, Widespread Issue Worth Understanding on Hybrid Models — Toyota Yaris Battery

If your hybrid's 12V battery keeps reading low despite a dealer telling you it "passed all checks," this is genuinely worth knowing: real, documented owner reports suggest Toyota's own dealer diagnostic test doesn't allow the battery sufficient time to stabilise after charging before testing it — meaning a genuinely weak battery can pass, only for the voltage to drop again within hours. It's worth understanding why hybrids are more prone to this: since the hybrid powertrain doesn't use the 12V battery for traditional engine cranking, manufacturers fit a considerably smaller-capacity battery, adequate for its job but with less margin for short journeys or extended standing.

Genuinely useful, official Toyota guidance worth following: if the car will be sitting unused for more than a few days, Toyota's own recommendation is to run it in "Ready" mode for around an hour a week. It's also genuinely important to avoid leaving the car in "Accessory" mode, since this can flatten the 12V battery within just a few minutes on some examples.

If the problem is genuinely persistent, it's worth pushing for a proper cell-level health check rather than accepting a simple charge-and-return: one documented case saw Toyota's own diagnostics find genuinely damaged cells, resolved with a warranty replacement using a higher-capacity unit, after which the problem stopped entirely.

Toyota Yaris Battery: The Part Everyone Blames First, Not Always Correctly

A Toyota Yaris that won't start gets blamed on the battery more often than any other component, and it's right often enough to make that assumption a reasonable first check. But it's not always the actual cause, which is worth knowing before spending money on a replacement that doesn't fix anything.

Before you buy: battery size, capacity and type (standard vs AGM/EFB for stop-start systems) vary by trim and engine. Always confirm against your VIN before ordering.

Toyota Yaris Battery: What It Does

The Toyota Yaris's 12V battery provides the power needed to start the engine and runs electrical systems when the engine isn't turning. On cars with stop-start technology, the battery works much harder than on older designs, since the engine switches off and restarts far more frequently — which is exactly why these cars need a specific AGM or EFB battery type rather than a standard unit.

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Toyota Yaris 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 Toyota Battery

The same part, covered across other Toyota models.