I have a 1992 softtail fxst and the battery is not being recharged after I ride it for a while it just dies, its a new battery so when I use jumper cables it will start but dies after a while...help

Needs new or recharged battery.

Possibly a dirty kill switch contact.

Battery is probably bad, 12.35 volts is only a 50% charged battery and this is a surface charge you have tested so it probably is a no good battery and as soon as any load is put on it it drops further. Replace it with an HD AGM battery. Otherwise recharge it and do a load test on it and see what results you get then

I would check the ground at both ends check your battery power wire also the plug that goes into the starter relay and you may just get a new relay or swap with known good relay last I would check the starter button on the handle bar you really checking for clean connections that's what I would do,, best of luck ,,

Have you tried jumping it? If jumping it gets it started and it dies after you take jumper cables off then you have a bad alternator. Which in turn your battery will not get recharged from your alternator like it should. Hope this helps!

Ok, it sounds like the proverbial "bad battery" to me. Although you say you measure 12 amp (I think you actually mean volts here) this doesn't tell you the condition of the battery. You can take a 9 volt battery that will not run the device it's in and measure it with a volt meter and it will measure 9 volts most of the time. Now, when you put a load on that battery, the voltage drops to almost nothing. This is because your volt meter cannot "load the battery. The same happens with your bike's battery.

Take your battery out of the bike and take it to an automotive parts store, Ask them to "load test" the battery. They'll charge the battery for a while and then put a "battery load meter" or "carbon pile" machine on it and put a load on the battery exactly like your starter is doing. Only now, you have a meter on the machine to show you what it's doing. You can do the same thing using you voltmeter. Connect it "across" the battery, red probe to positive, black probe to negative and press the start button. If the voltage drops below 10.5 volts, your battery is no good.

I would also suggest that you never use on to the "jump start" battery chargers in an attempt to start your bike. Your newer bike has delicate electronics that can be easily damaged by "spikes" of voltage that these devices are known for creating. You're better off push starting the bike. If the bike won't start with a regular pair of jumper cables and another battery, Go buy another battery, It'll be cheaper in the long run. Those electronics are very expensive and you cannot diagnose them yourself.

Good Luck and Ride Safe
Steve

30 psi front
36 psi rear (single rider)
40 psi rear (dual riders)

Replace the battery and clean terminals. It sounds like you have a dead cell in the battery.

Check your fuel petcock, check the vacuum hose to the petcock. Make sure it is not cracked or not sealing well at each end. Hope this helps.

JP