Welp, my battery doesn't stay charged and dies while riding. I am trying to think of what all could be wrong.

I replaced the rectifier with a brand new one from Partzilla (OEM for the DT175B).

Things that I guess could be the cause:

• The voltage regulator I added to stop blowing up headlights
• The blinker relay I swapped in since adding a new rectifier made my blinkers stop blinking with the original relay.
• The headlight bulb is a 35W instead of 25W
• The horn doesn't always work. Maybe it's got an issue where it's drawing power?

I'm not sure what else to look into for it. Maybe the wiring contacts need a good cleaning because they're adding resistance and stopping the charge from being juicy enough for the battery?

I am using a new SLA battery instead of a flooded one.

It charges fine on the battery tender and the bike is fine for about 3 hours of riding and then I realize I have no blinkers/lights anymore and I get to resort to hand signals and being honked at/ flipped off while turning.

I'm guessing your in the US & that your tail light runs of the battery. With 35 watt headlight instead of 25 it probably leaves nothing to keep the battery charged. I used to connect an ammeter between battery negative & earth. The meter i used started from a central position so i could see discharge if and & how far i needed to be revved to a least hold its own or hopefully give a positive charge. That way you can see straight away things like stop light bulb & flashers as to how much they draw. Go back to 25/25 headlight or even go to 20/20 or 15/15 if easily found. We used to have those options in NZ where i am & our tail light ran off the magneto long with the headlight. With your magneto driven headlight the lower wattage bulb the brightest the light & the regulator you say you fitted will stop them blowing but keep them at a bright limit, plus leave plenty in reserve for battery charging. Even flashers-- if you can get away legally with lower wattage. We ran 8 or 10 watt flashers instead of 17watt i've seen on some bikes. We also could get away with 10/3 tail light--10 stop light & 3 tail light, where 21/5 might have been original. I'm a bit lost as to how much the charging is limited by the single wire regulator but you could try it disconnected to see if the charging goes up & up the higher you rev it compared to with it connected up. You'd need to be careful doing that if you ran minimum wattage bulbs though as could blow them, but should be safe trying that with original wattage bulbs if say 25/25 is original.
See what others say. Oh, & i've seen people fit a 12 volt headlight bulb through being accidentally sold the wrong bulb as the writing on them can be difficult to read sometimes & that would be bad for charging. All in all it's not a strong charging system on your model or any of the smaller magneto model trail bikes.
After that long winded story--just go back to you original 25 headlight & that might leave enough for keeping battery up. Also i'm now thinking you might have the bigger bulb with 3 pin locating locking compared to one locating tang as don't think the bulbs i'm talking go up to 35 & also don't think the 3 pin locating type go down to 20 or 15. Confused--hell i am lol.

I want to try riding around with the headlight off (even though its illegal. Maybe in a parking lot), and see what happens.

I thought I had ordered 25W ones but accidentally got 35W, and noticed this while trying to figure out what might be wrong.

I replaced the original bulb type wit one of those newer halogen ones. Unfortunately I don't have a MM right now to test anything so I am going to poke around a bit and see.

The light bulb was my thought too, and I might mess with it once it stops being 90+ degrees out!

If I remember correctly, you've had this issue for a long time? Rectifier could be in backwards from a previous owner? (This would cause battery to drain through stator and could damage stator coils. Also would kill the battery.) Headlight switch could be bad and not connecting correct stator charge wire to rectifier? Or charging coil could have a bad connection or be bad?

Note that with lights off, you're using a different stator charging coil than with lights on.

Easiest test is check battery voltage with bike off. Start bike and rev, battery voltage should increase slightly. Test with lights on and off.

Manuals have troubleshooting.

Multimeters can be found cheap. Get one. Harbor Freight sometimes has them for free with coupon. Ebay has them for less than $10. I'd recommend getting a quality meter, but a cheap one is better than nothing.

Good luck!

My opinion is: The stock charging system is not designed to charge batteries that need a charging voltage greater than the battery's normal output.

If you take the stock lead-acid battery, add electrolyte to it, then walk away.... in a short time it will begin producing voltage all by itself. When you place that in a Yamaha Enduro (without electric start) the charging system will add small amounts of voltage to keep it charged while the engine is running.

My opinion is: Any battery that must be charged before use, needs a voltage greater than the rated output to charge them. Like a 6v gel cell battery needs 7v to charge it.

If your rectifier is bad or installed wrong, the AC voltage going to the battery may kill it. I say 'may' because I have never tested it. Theoretically, it will kill the battery... but I have never tried it.

My opinion is: The headlight voltage regulator, if installed correctly, should have no effect on the charging circuit.


(My opinion on this subject is based upon knowledge I have gleaned over time. I have not studied this in-depth, so that is why I say 'my opinion'.)