The Honda 400EX uses a 12-volt sealed lead-acid maintenance-free battery, typically around 6 amp-hours. Exact capacity can vary by year and trim, so check the labeling on your battery or the OEM spec for your model.
The Honda TRX400EX is a popular sport ATV whose electrical system relies on a compact, sealed 12-volt battery to start the engine and power lights and accessories. This article explains the battery type, how to identify the correct replacement, and practical tips for replacement and maintenance.
Battery type and specifications
The essential details you should know about the 400EX battery are summarized here. The model uses a standard 12-volt sealed lead-acid battery with maintenance-free design. Capacity is typically around 6 amp-hours, though some years may use slightly more or less. Always verify the exact rating on the battery label or in the owner's manual for your specific year.
- Type and chemistry: 12-volt sealed lead-acid (maintenance-free), commonly described as SLA/AGM in modern units
- Voltage: 12.0 V nominal
- Capacity: commonly around 6 Ah; some years may be 5–8 Ah depending on production batch
- Form factor and terminals: compact ATV battery with standard positive and negative posts; ensure correct polarity when replacing
- Replacement notes: use OEM-recommended battery or a compatible aftermarket SLA battery with similar ratings; verify fit in the battery tray
These specifications influence replacement options and charging requirements, and they help ensure the ATV starts reliably in all seasons.
Replacing or maintaining the battery
When it's time to replace or maintain the battery, follow these steps and guidelines to ensure safety and reliability.
- Turn off the quad and remove the key; disconnect the negative terminal first, then the positive terminal to avoid short circuits.
- Remove the seat and any covers to access the battery compartment; disconnect the cables and remove the old battery.
- Inspect the battery tray, cables, and terminals for corrosion or damage; clean terminals with a wire brush and apply terminal grease or dielectric grease as needed.
- Charge the replacement battery with a charger appropriate for sealed lead-acid batteries, using a slow or maintenance mode to avoid overcharging. Do not exceed recommended charging current or voltage.
- Reinstall the battery, reconnect terminals in reverse order (positive first then negative), seat the battery in place, and replace covers. Start the engine to verify operation.
Regular maintenance, such as keeping terminals clean, ensuring a full charge for storage, and using a compatible charger, extends the life of the battery.
OEM vs aftermarket considerations
OEM Honda batteries are designed to fit the TRX400EX precisely and maintain consistent performance. Aftermarket SLA batteries can offer comparable performance at a lower cost, but always verify the positive/negative terminal layout, capacity, and dimensions to fit the battery tray and wiring harness.
Year-to-year variations
Battery capacity and form factor can vary slightly by production year and region. If you own a specific year of the Honda 400EX, consult the official parts catalog or your service manual to confirm the exact battery group size, capacity, and terminal layout.
Summary
In brief, the Honda 400EX relies on a 12-volt sealed lead-acid maintenance-free battery, typically about 6 Ah, with some year-to-year variations. Replacement with OEM or compatible aftermarket SLA batteries, careful handling, and proper charging will keep starting and electrical systems reliable. Always refer to the owner's manual for your exact model year to confirm the correct battery specification.