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January 19, 2014
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The KTM is the only motocross bike to come with a battery, because it is the only motocross bike to come with an electric starter. The upside of electric starting is that you just press the button and go. The downside is that the starter motor and battery add 5 pounds to the KTM’s overall weight. (Surprisingly, it still isn’t the heaviest bike in the class.)

When you buy a new KTM, there is a 4.0-amp lead-acid battery in the bike. The stock Yuasa YTX4L-BS battery weighs 3.71 pounds (and the optional 5.0-amp battery for the 450SXF weighs 1 pound more). It is possible to put in an accessory battery that will be much lighter, much stronger and have a longer lifespan, but it won’t be a lead-acid battery. What will it be? Lithium-iron phosphate.


Don’t confuse a lithium-iron phosphate (LFX) battery with a lithium-ion battery (more specifically, a lithium cobalt-oxide battery). Lithium-ion batteries are most commonly used in computers, cameras and phones. A lithium-iron phosphate battery has a higher resistance to thermal runaway, longer calendar life, quick recharge rate, five times as many available discharge cycles, a higher peak-power rating and costs less.

LFX batteries (also called LiFePO4 batteries) contain no poisonous lead, no acid and do not create gases during charge (as traditional lead-acid batteries do). There are no liquids in an LFX battery, which means that nothing can leak, and you could put it in your bike upside down if you wanted to. Compared to a lead-acid battery, LFX lithium batteries are lighter and deliver a more powerful punch to the starting system. It should be noted that most of the lightweight batteries made for KTMs are iron phosphate, so this isn’t a selling point over the competition.

Most KTM motocross racers switch to lithium-iron phosphate batteries to save weight. Lots of weight. Depending on the number of amp hours you choose, the weight savings can exceed two pounds. It would take about $2000 worth of titanium to save that much weight on your KTM.


What are the differences between lithium-iron phosphate and lead-acid batteries?

     (1) The LFX batteries are smaller and lighter.

     (2) LFX batteries hold a charge much longer.

     (3) As the battery warms up, it seems to gain amperage and spin the engine faster.

     (4) Since there is no lead or acid in the lithium-iron phosphate batteries, they can be disposed of more easily; however, remember to discharge them fully before throwing them away.

     (5) Lead-acid batteries are extremely toxic thanks to their acid.

     (6) A lead-acid battery has a lifespan of 1-1/2 to 3-1/2 years. An LFX battery will last twice as long.

     (7) Another plus is that because of the lack of sulfation and slow-self discharge, an LFX battery can sit for months at a time and still be almost fully charged.

The amp-hour (Ah) rating for an LFX lithium battery is not the same as for a typical lead-acid battery. An LFX battery uses 100 percent of its storage capability (measured as amp-hour, or Ah), while a lead-acid battery typically only uses 30 percent. So a 2 Ah LFX battery has the equivalent capacity of a 6 Ah lead-acid battery. Because of its setup, an LFX battery can go to 80 percent discharge without damage and still retain more cranking ability.

In cold weather (under 40 degrees Fahrenheit), LFX batteries don’t generate as much power initially as lead-acid batteries. However, an LFX battery will get stronger rather than weaker as more starting attempts are made. Once the battery has warmed up, it will provide full power regardless of the outside temperature.

To help KTM 300XC battery life the KTM engineers invented a blow-by port that lessens engine compression during starting but is covered up by the power valve as soon as the engine starts. Aditionally, the KTM 450SXF is the only bike in the KTM line to come stock with a normal 4 Ah battery and a 5 Ah for cold weather.


You can recharge some LFX batteries with a lead-acid battery charger; however, you should never use a charger/tender if it has an automatic “desulfation mode” that cannot be turned off. Deltran Battery Tenders do not have a desulfation mode. Even though LFX batteries maintain a charge longer than a lead-acid battery, they still need to hold at least a 20-percent charge. A fully charged LFX can sit for a year or more and still retain adequate starting capacity without damaging the battery. Thus, on a motocross bike, where no current flows when the engine is off, you should never need a battery tender. Follow the instructions that come with the LFX battery, because some LFX batteries must be charged with a special charger.


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