Razor MX350 / MX400 Battery Replacement: Which 24V Battery Fits and How to Swap It
If your Razor MX350 or MX400 only runs for a few minutes, crawls up hills it used to climb, or the charger light turns green almost immediately, the battery pack is almost certainly done. The good news: swapping the 24V pack is a 20-minute job with a Phillips screwdriver, and it brings the bike back to how it rode when it was new.
Which battery fits the MX350 and MX400
Both bikes run a 24-volt system made of two 12V sealed lead-acid (SLA) batteries wired in series. The pack is sold as a complete unit with the connector already attached, so you are not soldering anything. The pack we stock fits the Razor MX350 version 33 and up, every version of the MX400, the Pocket Mod version 45 and up, Rambler 12, RSF350 and the Indian eFTR Mini, because those models share the same battery tray and plug.
Find your version number on the sticker under the frame or on the battery cover. If your MX350 is version 42, note that Razor used a slightly different pack for that single version, so double-check the sticker before ordering. Older MX350 bikes (below version 33) use a different connector; message us with your version and we will confirm what fits.
What to expect from a fresh SLA pack
Full charge takes roughly 8 to 12 hours the first few times; SLA packs need three or four cycles to reach full capacity.
Run time on a new pack is typically around 30 minutes of continuous riding, less with a heavier rider or lots of hills.
SLA batteries do not like sitting flat. Charge after every ride, even a short one.
Tools you need
Phillips screwdriver
10 mm wrench or socket (some versions use hex bolts on the cover)
A rag to wipe out the battery tray
How to swap the battery, step by step
Turn the power switch off and unplug the charger.
Remove the screws holding the battery cover (the plastic panel below the seat) and lift it off.
Unplug the battery connector from the bike harness. Squeeze the clip and pull straight; never yank the wires.
Lift the old pack out. It weighs around 10 pounds, so keep the bike steady.
Wipe the tray and check the harness plug for green or white corrosion. Clean it with a little contact cleaner if needed.
Set the new pack in the same orientation, plug it into the harness until it clicks, and refit the cover.
Charge the new pack fully before the first ride, then ride it to about half and charge again for the first three cycles.
Recycling the old pack
Sealed lead-acid batteries are accepted free at most auto-parts stores and battery retailers. Do not put them in household trash.
Common questions
Can I use a bigger battery for more run time? Not in the stock tray. The MX350 and MX400 battery bay is sized for the standard two-battery 24V pack, and a higher-capacity pack will not fit without modifying the frame and the harness, which we do not recommend on a kids' bike.
Do I need a new charger with a new battery? Usually not. If the old charger shows a red light while charging and green when done, it is fine. Replace it only if it shows no light or goes green instantly on a flat pack.
How long should a new pack last? With a charge after every ride and no long periods sitting flat, a 24V SLA pack in an MX350 typically gives two to three riding seasons before run time drops noticeably.
Buy it here
Battery 24V for Razor MX350 (V33+), MX400, Pocket Mod, Rambler 12, RSF350 and Indian eFTR Mini — $167.95. Every part ships from our warehouse in Miami, Florida, and code SMB10 takes 10% off at checkout. Questions about fitment? Message us with your model and version number before you order.
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