A 3 month old battery loses its charge with 15 miles

Hi there folks.

i bought a new battery in April 2026 for my 1981 KZ440 LTD. The battery model is Yuasa AGM  Motorcycle Battery YTX7L-BS

it took around 5 hours to charge, after being left in the unused bike, charged after receiving it in April then installed. After an 8 mile trip into town the bike stalled on low revs. I got it home after hill starting a couple of times.

it appears that the battery is simple a dud, however I’d like to test it to confirm, as perhaps there is a wider electrical problem that might be draining the battery while it is unused.

id be grateful please for any advice about checking the integrity of the battery and/or checks I can make on the bike to see if the cause of the battery drainage lies elsewhere. 

very many thanks. James

Use a volt meter set to DC and jumper across the battery to read voltage.  Start up the bike and rev to 5000 rpm, to see what the charging system is doing.  A proper charging system will charge the battery at about 14 - 14.5 VDC at 5000 rpm.  Chances are high that you are not getting much if any charging.

Thanks Nessism.

I’ll recharge the battery and do that.

in the meantime, would a good battery 3 months old, without any charging, last more than 15 miles of typical riding? I would have thought so, making me think it’s a dud battery, but I may be wrong. 

thanks again. 

Jimbo68 wrote:

Thanks Nessism.

I’ll recharge the battery and do that.

in the meantime, would a good battery 3 months old, without any charging, last more than 15 miles of typical riding? I would have thought so, making me think it’s a dud battery, but I may be wrong. 

thanks again. 

Probably not to be fair

Battery charged. I won’t get a chance to start her up and measure the voltage until next week. 

I’ll be back in touch then. Cheers. 

Wookie58 wrote:

Jimbo68 wrote:

Thanks Nessism.

I’ll recharge the battery and do that.

in the meantime, would a good battery 3 months old, without any charging, last more than 15 miles of typical riding? I would have thought so, making me think it’s a dud battery, but I may be wrong. 

thanks again. 

Probably not to be fair

I have a crappy story for this. My 1000 csr had the stator go bad on it. I didnt realize it yet and went to my brothers work 8 miles away to pick up something because he apparently owns the whole garage and can take stuff wherever he wants... 

Wait, where was I?  Anyways I had the bike idling in the parking lot and when I put on the brake to mount the bike it died immediately. I ended up getting my bike jumped by a random neighbor after trying to push start it a lot.

I started driving it hope and it lost power really bad to where I can only imagine it barely had any spark where i was almost full throttle. 2 miles from home I got stopped by a stop sign and the bike died again.

This time I wasnt so lucky and had to push it the rest of the way home with sticky front brakes on a hilly back road... I dont want to have to do that again. All to say I made it maybe 8 miles on a battery with an unknown charge and about 5-6 miles on a very dead battery.

Yeah, that's one reason I have a digital voltmeter on my dash.
If my voltage drops below 12.6v while riding, I can start making plans.
I had this happen once and figured I could make it home if i didn't stop.
A stator wire had come loose.
If I didn't have the gauge, the bike would have died miles from home.

I got this idea form Allen Millyard

 

After a full charge and 5 days passed without switching the bike on, I measured 13.5V before starting it up.
at 5000rpm I measured the same voltage: 13.5V, so if it should measure more I assume it is not being charged as you suspected.

can you please advise what I should look at next?

thanks again. 

Disconnect all connectors on the voltage regulator. You can ohm out the stator from there. Should be less than 1 ohm between yellow wires.Also clean the connections before reconnecting.

Thank you.

What do you mean by “You can ohm out the stator from there“ please?

Removing the pulley cover I discovered some poor wiring. Some blackening too on white insulation tape and on the wiring.
I separated the ‘yellow’ wiring and measured 88V AC from the alternator at 4000 rpm. 
Resistance between each of the yellow cables in turn from the alternator and ground measured infinity. 
I’m unhappy with the wiring so I will sort that out. If anyone knows the # of strands required in each wire from the alternator I’d appreciate it tho I think I can figure it out.

One question: one of the yellow alternator wires is cut back almost to the entry point through the grommet to the alternator. It is also partly severed.  If I can remove the alternator cover (there are at least 4 badly chewed screws so I am not hopeful at this point), can I replace this yellow cable readily where it terminates on the alternator?

 

 

 

If you can't get the chewed up screws out with an impact, drill the heads off with a left hand drill bit. The screws usually start unscrewing from the heat just before the head pops off. If they don't there's enough screw left after pulling the cover to work with. Most of the time you can unscrew the remaining part with your fingers.