battery voltage drop?

[axldk6]

yup did a search didnt find any info, here's I go: new problem showed up.  when I key on bike the battery voltage drops almost in half. when I turn the key back off it starts to climb backup. (  found this out  after I could not get  it to kick /fire over. and re checked the plug gap/points gap, and did not have spark at the plugs). the bike I have had for 5? months so is still a project bike and the battery and points and condensor are 4? months old. I DID get it to fire off for a few this morning with my jump starter then it ran out of juice too.  thoughts on the voltage drop with key on? cheap battery from e-bay. tia     

[axldk6]

fyi, when I first got the bike up and running a couple months ago it was charging too. with the same battery.

[m in sc]

honestly sounds like a bad battery   

[axldk6]

yea what I am thinking, I did say battery more than once.  mark , what is a good replacement one?

[m in sc]

i run alarm batteries, prob not the best person to ask, but i get 5-8 years out of them.

 I'll be honest, prob worth checking if there's a parasitic drain or failing component somewhere as well. need a fresh battery, and check charging voltage. 

[axldk6]

I really dig wiring trouble shooting  guess I should start unplugging things , like my coils since I am doing your SV coil upgrade suggestion.

[m in sc]

yup. prob a good idea. could be as simple as a disconnected wire in the headlight bucket or a brown swapped. fwiw, I chased an intermittent power lead short on my 1st rd for almost a year before I found it.

[sav0r (CL MotoTech)]

If the ignition is on the voltage drop is from exciting the coils. They don't like to function under like 10.5v which explains the jumper pack. Probably a bad battery.

[irk_miller]

I would load test the battery before assuming a bad battery is your issue.  Just turning the ignition switch on shouldn't drain it that quickly unless your exciting the starter solenoid. The ignition coils don't draw more than 4 amps.

[Jspooner]

I would load test the battery before assuming a bad battery is your issue.  Just turning the ignition switch on shouldn't drain it that quickly unless your exciting the starter solenoid. The ignition coils don't draw more than 4 amps.

Depends if he's got the headlight on or not.

[1976RD400C]

When you do a voltage reading make sure the test lead is pushed right on the battery terminal and not on the cable. That will prove its accurate and a bad cable connection is not giving you a false reading.

[axldk6]

thanks for the help guys, like an old VW bug the wiring has been fiddle farted with over the years. I did load test the battery after charging it back up. Used an 1157 bulb, drained it down . looks like I got ebayed as the seller wont work with me. So , need a new one . But what is a better version?

[sav0r (CL MotoTech)]

Just put an alarm battery as Mark suggests in it. At least until you have everything sorted, and even then it's a good reliable and affordable way to go.

[axldk6]

agree, just gotta find one to fit in my bike, most are long rectangle , guess I could bend the front tabs on the battery box?

[SoCal250]

I have a couple of these in my bikes. I've been using alarm batteries since the old days when we used to get them from Radio Shack. Just change your lead connectors to F1 terminals or make adapter pigtails.
https://www.amazon.com/dp/B079ZCJYP3