The battery on my 89 ninja 750 wont stay charged

3rd party battery?

Take it back to the dealer! they will check for free. It is one of those. Sometimes you get a new part that is still bad, it happens. Take it to any reputible dealer and like i said, they will check it for free

sounds like a short..any systems failing like headlight not working or something else?...i strongly suspect the alternator if there are no other issues with the wiwring being shorted..

hello carl...sounds like you might have a charging system problem. If you have a volt meter you can check it out. You can test at the battery. With the meter leads, red on positive, black on negative, you should have 13.5-14.5 volts direct current with engine at 3500 RPM. I hope this helps.

If the battery is good, check the connections, and fuses
How does it start?with no power

its not been charged by the alternator so you have to change the alternator is not a massive job to fix can be a diy job

you didnt mention anything to do with the carbs so try some "Sea foam".... purchase at Autozone ($10) pour 1/3 can to two gallons fuel and drive it around for a good 10 to 15 miles and get on it once in awhile, ride safe..if the carbs are dirty or clogged... they wont be after your ride..there might be a little hesitation your first couple of miles till it starts to work..it took my bike 10 miles before it cleared out..bump start your bike if you have to to get it going and keep it going till it clears up.

Check the water level in the battery and add water to cover the top of the plates. Charge the battery. Replace it if it will not take a charge. A weak battery can cause the problem.

YOU NEED TO TRICKLE CHARGE THAT BATTERY TILL FULLY CHARGED AT A RATE OF 1 TO 2 AMPERS IF THE BATTERY WONT HOLD THE CHARGE YOU WILL NEED A NEW BATTERY THE NEW BATTERY WILL NEED TRICKLE CHARGING AT THE SAME AMPER RATING FOR AT LEAST 16 HOURS THE REASON WHY YOUR LIGHT WHENT OUT IS NOT ENOUGH POWER TO SUPPORT EVERY THING FROM THE BATTERY