Stupid battery question

OK, I was told that you have to charge the battery in ktms. That they don't charge themselves while the motor is running like a car. This is coming from a guy who has a 400sx and put the starter on it. He has to trickle charge the battery before every ride (or after I guess)

Tell me this isn't true!

I have a 520 exc that has been started by the button for a year with no problems. Maybe the sx does'nt have what it takes to charge the battery.


I have an '03 525 EXC and my battery died after a day of riding and using the happy button. I could still kick the bike over which makes me think that the battery isn't required for the normal operation of the bike.

Anyway, when I got home I pulled the seat/covers/tank off and checked the votage accross the battery. It was around 11.4V. I started the bike and measured again. Still 11.4V !!! I finally decided to check the voltage regulator and BINGO, a wire had not been correctly inserted into the plug from the factory !! I reconnected it, kicked her over and now the voltage accross the battery measures 12.2V !!

So, the answer to your question is that the battery is constantly charged when the bike is running, and there should be no need to charge it unless it has run down by overuse of the starter or some phantom power sapper



I have a 02 400 exc. I have a Battery Tender charger with the supplied connector hooked up and stored in the airbox. I don't get to ride every weekend so when it's going to be a few weeks I hook it up just to make sure I don't have to use that kick starter. I haven't even tried kicking it just to see if it works. :)

Still have yet to put my 02 on a charger, and have never had to kickstart. I've heard that if you're running lights and a cooling fan with the stock stator and battery there are some issues.

I never had to charge the battery on my 520MXC and I always used the button....

All KTM's run some type of changing system, none are total lost type systems. The SX 400 has only a 40 Watt charging system (2.9 amps) but must be wired with a special made connector to a stock EXC rectifier / voltage regulator.

I have done this a dozen times on SX bikes. In fact one of them started as a 400 and is now a 520 (still retaining the 400 flywheel) with no starting problems for over 2 years now. Remember that any battery that sits over time will lose voltage and once a battery reaches <10 volts it starts the sulfate process which is very hard to recover. (Starts fine for only a few times, then appears the battery is dead.)

Bottom line, the small battery tenders with a floating voltage regulator is a good way to keep your battery up to speed. If you use any charge larger then 500 MA ( .5 amp) you may want to watch electrolyte level and total charging time. Hour or so, not overnight.

If you need help with the wire diagram or part numbers on voltage regulators, just drop me an email.


I have an '01 520 MXC and have never had to charge the battery, even after not riding it for 2-3 weeks.

All batteries self discharge over time and using a Battery Tender set up is so easy. I always connect my RFS up to a Battery Tender when in storage, it is cheap insurance. I have the provided pig tail connector permanently mounted to my EXC and just plug it in and forget it.

The RFS EXC electrical system is a dual AC and DC system and the stock rectifier is only a halfwave rectifier. In addition the stator is wound with 4 poles for the AC and 3 poles for the DC. Over a year ago I had my stock stator rewound using a different diameter wire with one continuous wire going to all 7 poles and a full wave DC rectifier (120 Watts DC only). I did this since I run a fan and it runs allot. The stock system uses the AC to run the headlight and tail light. The DC (3 poles halfwave rectified) is only about 25 watts max is used to TRICKLE charge the battery, however the fan also runs off the battery and over time will discharge the battery. In addition my bike is dual sported and I run full DC only electrics (I tossed all the stock wiring and stuff).

Dale at Trick Dual Sport can easily modify the stock stator using the existing stator wiring and pull all 7 poles into DC circuit use and when he adds a fullwave rectifier it will put out approx 90 Watts DC which is adequate for a full dual sport system and fan.

Contact Dale if your interested in a great dual sport kit and/or stator mod. :)



I only get to go riding about once a month. At that rate the battery will not hold a charge. I bought a Battery Tender cause it died after I let it sit for the first time. What a great product. Lets you know when it's charging, when it's full, and when it just trickling, and it won't overcharge.

I finally figured out what the story was on this when I called Baja Designs to try to get more light from my stator. The stock stator turns out 110 watts according to the manual. About half goes to charging the battery and the other to the light. If you run a brighter light than stock, like a 85 watt super white bulb, you will need more lighting power.

So I guess, it works pretty much like a car.

I trickle charged my battery when it was new and it needed a slight charge. I run both the high and low beam on (70 watts) most of the time with no problem. If I'm doing a lot of 1st gear riding and the fan is coming on a lot I usually turn off the headlight. Bike always starts - even after sitting for a couple of weeks. I think that I will get a battery tender for the winter. I kick started my bike on the very 1st ride after ~30 miles just to be sure that it worked and it started easily on the 2nd kick - hope I never have to use it again! :)

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