Yuasa Motorbike battery YT9B-BS 12V 8Ah (8.4Ah) (AGM maintenance-free)

The Yuasa YT9B-BS (often also referred to as YT9B-4) is a specialised AGM battery in a flat design. It fills exactly the gap between the very small YT7B and the larger YT12B. With a capacity of approx. 8 Ah (10h) or 8.4 Ah (20h) and a cold cranking current of approx. 115 A (EN), it is the standard power source for many mid-range motorbikes and maxi scooters, especially from Yamaha. It combines compact dimensions with high vibration resistance for single-cylinder engines.

Highlights at a glance

• Flat housing: At only 70 mm width it is significantly narrower than standard batteries (such as the YTX9-BS), making it ideal for slim tail frames or tight fairings.
• AGM technology: The acid is bound in the glass mat, making the battery leak-proof (up to 45° tilt) and extremely vibration-proof – perfect for the "vibrating plate" Yamaha XT660.
• Maintenance-free: Thanks to VRLA technology (valve-regulated), the system is hermetically sealed after the first fill; topping up with water is not possible and not required.
• Starting power for singles: Reliably delivers the necessary current (~115 A) to turn large single cylinders (660cc) past top dead centre.
• Long service life: The sulphation inhibitor and robust construction ensure good durability, even in seasonal use (with proper care).
• Yamaha standard: Specially developed as original equipment for the popular 660 models and the T-Max scooter.

The standard for Yamaha XT660 & T-Max

The YT9B-BS is the indispensable battery for owners of a Yamaha XT660 (R, X or Z Tenere) as well as the Yamaha MT-03 (the old 660 version). These single-cylinder motorcycles need a vibration-resistant battery that fits the narrow compartment. Early models of the maxi scooter Yamaha T-Max 500 also use this special type.
 

Features

FAQs about the Yuasa YT9B-BS

What is the difference to the YTX9-BS?

This is the most common confusion. Both are the same length (150 mm) and the same height (105 mm). The difference is in the Width.

• YTX9-BS: 87 mm wide (the "thick" standard, e.g. Kawasaki Z750, Honda CBR).
• YT9B-BS: 70 mm wide (the "slim" special version, e.g. Yamaha XT660). If you ride a Yamaha XT660, the YTX9-BS will not fit into the compartment (too thick). Pay close attention to the "B" in the middle (YT9B).

What does YT9B-4 mean?

This is technically the same battery as the YT9B-BS.

• YT9B-BS: "Bottle Supplied" – The battery is supplied dry pre-charged with a separate acid pack (shipping standard).
• YT9B-4: Often the code for the already factory-filled and sealed version (Factory Activated). Dimensions and performance values are identical.

Can I install the battery lying down?

Yes, to some extent. As it is an AGM battery, the acid is bound. Many manufacturers (like Yamaha in the T-Max or Ducati in other models) install this battery type horizontally. It is important that after filling (in the BS version) the battery rests for about 1 hour and is then sealed 100% correctly with the sealing strip. It is then leak-proof.

Is the starting power sufficient for my 660 in winter?

The YT9B-BS is sufficiently dimensioned for the 660 engine, but does not have huge reserves. In very cold temperatures and with viscous oil, the starter has difficulty with single-cylinder engines. Make sure to recharge the battery regularly in winter (maintenance charger), as even a small voltage drop can mean the starter won't turn the piston over compression.