What size battery is in a 400EX?

The Honda TRX400EX uses a 12‑volt lead‑acid battery, typically around 6 to 8 amp-hours, with the exact size depending on the model year. To be certain, check the OEM specification for your specific bike.

In this article, you’ll find how to identify the correct battery size for your TRX400EX, what replacement options fit, and practical tips for installation and maintenance.

Model-year variations and typical specs

Most TRX400EX models rely on a compact 12‑volt battery that fits a small tray under the seat. Common capacities are 6 Ah (typical for standard starting) or 8 Ah (higher cranking reserve). Replacement batteries frequently fall into the YTX7L‑BS family (about 6 Ah) or the YTX9‑BS family (about 8 Ah). Exact fit depends on the year and the OEM part number, so confirming the correct spec is important.

Since Honda updated some components across production years, verify the exact part number for your year before purchasing a new battery to ensure proper fit and performance.

Next, here are the practical options and what to look for when choosing a battery for your TRX400EX.

• 6 Ah option: YTX7L‑BS or equivalent, a compact size suitable for standard starting and moderate electrical loads.


• 8 Ah option: YTX9‑BS or equivalent, higher capacity for better cold-weather starting and additional electrical demand.

Both 6 Ah and 8 Ah batteries are available in flooded (maintenance‑type) and AGM (maintenance‑free) formats. AGM batteries are often preferred for ATVs due to better vibration resistance and no need for regular electrolyte checks.

How to verify the correct size for your model year

To confirm the exact size for your TRX400EX, use these steps:

1. Consult the OEM parts fiche or owner's manual for your model year to obtain the exact battery part number and rating.


2. Inspect the current battery: read the label for voltage (12V) and capacity (Ah) to match the replacement.


3. Measure the battery tray space and terminal layout (positive/negative positions) to ensure the new battery will fit and connect correctly.

Following these steps helps avoid mismatches that could lead to fit issues or electrical problems.

Replacement considerations

When replacing the battery, consider installation and performance factors beyond just the Ah rating to ensure reliable starts and long life in varying riding conditions.

• Battery type: AGM batteries are maintenance-free and more vibration-resistant, making them a common choice for ATVs.


• Cranking amps: Choose a battery with equal or higher cold-cranking amps (CCA) than the OEM specification to ensure reliable starting in cold weather.


• Terminal orientation and fit: Verify the positive and negative terminal placements match your wiring harness and that cable lengths are sufficient.


• Vibration and mounting: Ensure the battery is securely mounted to minimize movement and electrolyte spillage in flooded models.

With the right type and fit, the TRX400EX battery should deliver dependable starts across seasons and riding styles.

Summary

In short, a 400EX uses a 12‑volt lead‑acid battery, commonly 6–8 Ah, with exact size varying by model year. To source the correct replacement, verify the OEM part number for your year, compare your current battery's label, and measure the tray if needed. Consider upgrading to an AGM type for maintenance-free operation and robust performance in rugged riding conditions.

What size battery does a Honda 400EX take?

Mighty Max Battery YTX9-BS Replaces Honda ATV TRX300EX TRX400EX 300EX 400EX CBR900R RR.

What kills batteries faster?

Than the wire. Charging. As we saw before heat accelerates your battery aging the latest independent tests show wireless charging can degrade your battery up to 30% faster than the wire charging.

What is the size of the battery?

Battery Size Chart

Are ATV batteries six or 12 V?

Your battery or your ATV owner's manual should tell you the ideal voltage. Most batteries need somewhere between 12.6 and 12.8V. Some need more. No battery is running well with less than 12.6V.