What else should I test?

My 79 KZ1000ST just died earlier while riding and when I checked the battery it was completely dry. I bought a new battery and everything works fine. My question is, is there anything else I should check? It seems weird that it would just die while riding, not starting I could understand but it seems like there might be another problem here. I know in the past when i've had charging issues with my car i've ended up replacing the alternator as well. How would I go about checking that on this bike? I know next to nothing about electrical work so any help I can get would be greatly appreciated.

Yes, a bad battery can do that. How often do you check the fluid level? If it has been a long time, then nothing else may be bad. If you check it often, and all the fluid boiled off in a week or two, then the system may be over charging.
The factory service manual explains the diagnostic procedures. I do not know the specifics for your bike, but if at 3000 or 4000 rpm, there is no more than 14.5 volts at the battery, you are probably ok. Be sure to use the testing procedure for your year and model.

I always test the charging system when I'm looking at older bikes or cars. I've just been working on the charging system on my KZ750, so I might be able to give you some insight.

If the battery has dried out during normal use, it's probably as TexasKZ has alluded to - that your bike might be overcharging your battery. If you don't have a multimeter, I suggest you buy one, or doing even simple electronics will quickly become a lot of work.

Check your voltage across the battery when the bike is running, and again at higher revs. The manuals suggest that it should be 'around 14.5V', but that is quite high for any vehicle these days. Closer to 14V is ideal, and personally I wouldn't want any higher that 14.5.

Now, switch on your headlight, and repeat the same procedure. Since the headlight draws power, you would expect the voltage to drop. But it doesn't - this is one of the quirks of the KZ electronics. From the wiring diagrams I've found on google, the cause is the same as what I found with my KZ750. The regulator measures the voltage of the accessories circuit (a brown wire) to determine the voltage of the battery. In an ideal world the accessories has the same voltage as the battery, but in the real world any accessories used will lower that voltage, so the regulator will charge higher to compensate. On top of that, if there's any corrosion or loose connections of your plugs, fuses or wires this will make the problem even worse. In my case, the charging voltage was about 14.8 volts (too high) and with the headlight on about 15.2V (way to high - battery boiling territory).

If you have this problem, clean all your connections and clean all your fuses, including the battery connections and grounding wires That should increase the voltage of you accessories circuit. If it's well above 14.5V even after cleaning all your connections you probably need to replace your regulator and hope that the new one provides a lower voltage.

What I ended up doing is wiring in a relay, such that the accessories circuit would open a path directly from the battery to the regulator so that the regulator was reading the battery voltage, not the accessories voltage. This dropped my charging voltage back down to a respectable 14.2V whether the headlight is on or not.

Thank you both for your insight. I don't know how long the battery had been dry, the first time I had ever checked it was when I had this issue. It does have a date written on the side form the PO of 3/22/14. That doesn't seem old enough to have problems. I will test the system and see what I see.

For an ordinary lead-acid battery, three years and done is not unusual, especially if the fluid has not been kept at the proper level.
I've had really good luck with AGM (absorbed glass mat) batteries. My ZRX came new with one that lasted 10 years, and the replacement is now 7.

newjack213 wrote: Thank you both for your insight. I don't know how long the battery had been dry, the first time I had ever checked it was when I had this issue. It does have a date written on the side form the PO of 3/22/14. That doesn't seem old enough to have problems. I will test the system and see what I see.

Unlike modern car batteries, the lead /acid batteries in the KZ models are not maintenance free. If you had neglected checking the battery fluid level since March 2014 it is no wonder it was dry. I'm surprised it didn't fail much sooner. You need to check the fluid level in the lead/acid KZ battery once a month or so and top it off to the proper level with distilled water. Ed

Thanks for the suggestions everyone. I tested the system this morning and am getting a respectable 14.5 V @ 4000 RPM just like the manual says. I replaced the old battery with a Super Start Platinum AGM battery. I'm hoping for it to last 10 years like yours TexasKZ, especially when it cost me $97 at O'Reilly's. Let's see if i can make it though the Bun Burner 1500 that i'm starting at 6am tomorrow without any other issues.

A bun burner on a 40 year old motorcycle :ohmy:

You are a stouter man than I. Good luck.