Battery question.

On my 82 kz440 I just purchased a new battery probably 3 months ago. This morning I got on the bike and it started fine then as I was going down the road it started sputtering and lost power. I pulled over to a gas station thinking I was out of fuel. I had a full tank. When I went to start the bike again it would not turn over, just clicked. Lights and horn worked and I could roll start it to get it home. What keeps the battery charged and what could be my issue? 

Firstly you need to measure the battery voltage "static" to see if it is a battery issue. If the battery is discharged then you need to measure the voltage across the battery with the engine running at approx 2000rpm (following push start) - the battery is charged by the onboard generator in the same way that a car does. Once you know if the issue is or is not battery related we can give you more to go on

Yeah,  it sounds like a charging system issue as you were able to start the bike and run it for a bit and then it shut down. The charging system should have been able to keep the bike running.
Take the readings Wookie suggested above and we'll see from there.

How do I go about testing the battery? A multimeter? I'm terrible with electrical issues. Sorry for the ignorance. 

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How do I go about testing the battery? A multimeter? I'm terrible with electrical issues. Sorry for the ignorance. 

Take the readings I suggested with a multimeter set on DC volts (you are not alone being challenged by electrical issues)

I should have between 12-14 volts across the battery without the bike running? I'm very confused. 

What type of battery is it & was it properly serviced before installing on the motorcycle?
If the motorcycle isn't ridden, the battery needs to be charged periodically.
I use a Ctek US 0.8 smart charger & VC97 digital multimeter. 

When the engine is off, the battery should be about 12.6 VDC. 
After charging, a good battery can be higher. up to about 13 VDC or thereabouts.
With the engine running, the voltage varies depending upon the rpms. ~12.6 VDC at idle to ~14.5 VDC @ 4000 rpms.

 

Put the battery on a charger and charge it up. If the bike starts and runs fine for a short time but shuts down while riding for awhile, the bikes charging system is bad. I would feel safer carring a spare battery to get me home.
You can get a volt meter for under $30. You don't need to be an engineer to check voltages. I didn't know motorcycling was possible without one.

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Put the battery on a charger and charge it up. If the bike starts and runs fine for a short time but shuts down while riding for awhile, the bikes charging system is bad. I would feel safer carring a spare battery to get me home.
You can get a volt meter for under $30. You don't need to be an engineer to check voltages. I didn't know motorcycling was possible without one.

Certainly not if you have a preference for a more "mature" machine 

I ride the bike ever single day. I got the battery from a Kawasaki dealer and it is the OEM for the bike. It is only 3 months old. I will put it on a charger tonight and see what comes up this weekend. 

So I pulled the battery and it ran 12.6 VDC on the bench. I've got it on a motorcycle battery charger right now. Sounds to me like the battery is fine though. Where do I go from here?

Look back at my first post, put the voltmeter across the battery with the bike running at approx 2000 rpm with the headlight on,the result will tell you if it's charging or not on the bike