Battery no power?

hi all I apologize if this is a duplicate post but perhaps someone here can help me out? I have a 77 750 twin and for some reason it wont turn over with just the battery, this is a brand new agm sealed battery that was fully charged by the the store while i waited. but as soon as i put a jump pack on it it starts right up with no issue. Any input on this is much appreciated

thanks in advance

Did the bike act the same way with the old battery?

Maybe you got a bad battery, it happens. Way to check for sure is put a voltmeter across the battery terminals and read the volts when you push the start button. A good battery should be 10-11v give or take. If volts drop to zero or some other low number, the battery is a no fricking good new one. I got 12 miles out of a Motocraft battery one time.

Check all of the large battery cables for being clean and tight, and the ones going to and from the starter solenoid. The starter motor connection should be tight too. Sometimes, battery cables develope internal corrosion, so if they feel "Crunchy" when flexed, it's time to replace them.

6 AWG (Ameican Wire Gauge) welding cable is larger than what came with the bike,and will provide more current flow. You'll need to have the correct terminals crimped/swaged on the end of the new cables. The welding supply store might be able to do this, but if not, go to a shop that works on electric forklifts, as they are usually creating new cables.

yes it was acting similar however my starter motor was bad previously as well and i just replaced that, i bought a better battery charger then what i had before im going to try it with with that before i go ripping out wires, and for the battery cables making a new one is that similar to replacing them on a car/truck? if so i already have the equipment to do that as i just did it on my durango
thanks for the replies all i hope to get pictures up soon this is my first bike and also my first project

Your bike's battery cables are about 8 AWG in size. If you can get new terminals, it should improve the current transfer. www.easternbeaver.com might be able to get new cables that will bolt in with no problems.

Make sure the grounding wire from the - side of the battery is attached to the engine and the mounting surface is good and clean. The starter is grounded through the engine and if the engine is not properly grounded then the starter will not function properly

baldy110 wrote: Make sure the grounding wire from the - side of the battery is attached to the engine and the mounting surface is good and clean. The starter is grounded through the engine and if the engine is not properly grounded then the starter will not function properly

I agree with Baldy and this is where I would go first. In fact I would check all your connections for cleanliness and tightness.

Does the new battery meet/exceed CCA specifications of the OEM battery.
Best to exceed cranking amps....

+1

Also, if as you imply, you try to start the bike from the battery starter you will probably fry your electrical system. A battery charger is not a substitute for a battery. Same with trying to start it from another vehicle that is running. Ed

i bought new cables to replace the old battery ones hopefully getting to it this weekend if the weather holds up, the battery was what i connected the jump pack to so