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

OEM Part Numbers

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

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.

The Part Everyone Blames First, Not Always Correctly

A car 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.

What It Does

The 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.

Fitment & Compatibility

Battery type and capacity differ between standard and stop-start equipped versions of the Yaris, and fitting a standard battery to a stop-start car can cause premature failure since it's not designed for the frequent cycling involved. Always confirm the exact battery type and capacity for your specific trim before ordering. Whether you're sourcing a replacement battery for your Toyota Yaris from a dealer, specialist, or online marketplace, always check compatibility against your registration or VIN before buying.

Common Faults

Symptoms of Failure

Slow or laboured engine cranking — often the earliest sign, especially noticeable in cold weather.
Dashboard warning light — a battery or charging system alert shouldn't be ignored, even if the car still starts normally.
Electrical accessories behaving oddly — flickering lights or a stuttering infotainment system can point to inconsistent voltage.
Stop-start system disabling itself — many cars automatically turn off stop-start when battery health drops, a useful early warning most drivers miss.

DIY Replacement Difficulty

This is generally an easy DIY job on most versions, though modern cars increasingly require a "battery registration" step using a diagnostic tool afterward so the car's charging system recognises the new battery correctly. Skipping this step on cars that need it can lead to reduced battery lifespan even with a brand new unit. Expect 15–30 minutes for the physical swap, plus registration if your specific car requires it.

OEM vs. Aftermarket

Reputable aftermarket batteries from established brands are widely regarded as a safe, reliable alternative to OEM parts, provided the type (standard, AGM, or EFB) and capacity match your car's requirements exactly. This is one part where matching the correct specification matters far more than the brand name on the case.

More Toyota Battery Guides

The same part, covered across other Toyota models.