Ktm 450 09 model Battery loosing charge after an hour ridding will not start on the button. Replaced battery still no good checked voltage when on bike under load it only shows 12.8v any help

Take the battery in to a vehicle battery specialist for checking. It will be a free service.
They will hook it up to a small machine that will load test it.
11.5V seems low to me.
If the battery is new it may still be dead and can be replaced under warranty. I had one go in 3 months and was replaced for free.

Your battery may bad. Unhook it,check voltage, charge it 24 hours. Check voltage, should about 12 volts. Let set 24 hours, check voltage , if not 12 volts, no good.

Thank you for contacting FixYa with your inquiry.
Thank you for contacting FixYa with your inquiry.
This is not an uncommon behavior and we need to locate the source of the problem and eliminate the things that are not effecting the issue.
Most probable causes: Battery, Starter Relay, Start Button, Starter.
Manually start the bike and take it for a good rip and see if the battery takes/holds a good charge for the rest of the day. If you don't have trouble starting through out the day then it's a good chance you may need to replace the battery. Recommend the use of a trickle charger to keep the charge up during the week when bikes in the garage. Part# 53 Frame Parts/Wiring Harness.http://cyclehuttktm.com/FicheFinderNew/FicheFinder.aspx
If your battery is known to be new or has a good charge, do you often hear a clicking sound. It might indicate your starter relay is wearing out or you have a short. Trace the wire harness and confirm insulation wear.Check starter wire and confirm the nut's tight with a good star washer. If relay - replace it. Part Number #58 Frame/Wiring Harness http://cyclehuttktm.com/FicheFinderNew/FicheFinder.aspx
If the battery is known good and the relay pulls in but the starter won't engage and you can hear it attempting you may have an issue with the starter being in a bind from some internal obstruction or just plain worn out. Pull it and check it. See if it engages off the frame. You may have to take it to an alternator shop and have it re-wound. New ones are spendy.http://cyclehuttktm.com/FicheFinderNew/FicheFinder.aspx
Starter Control Button: Reseat the connection and confirm it's engaging the relay. Part Number #69 chassis/Handlebar Controls. http://cyclehuttktm.com/FicheFinderNew/FicheFinder.aspx
Hope this helps you resolve your starting issue. If we can provide further assistance please advise,
Best regards,
TF

have the alternator bench tested for faulty rectifier diode pack
it may be charging the correct voltage but it is AC voltage and not DC voltage
in which case the battery will die quickly
next to check is the voltage regulator
it has to be 4.5-14.8 volts DC and if it in the ECM unit , will require a new ECM to fix

When the engine is running check the voltage at the battery. It should be over 13VDC or the battery is not charging and will go flat. The battery is charged by a stator under the flywheel and either the stator or the magnets on the flywheel have gone bad. this can be checked with an electrical meter as well. Stator output should be 13 or 14VDC on the red wire the orange or brown wire is for the headlights. All voltage checks should be tested with the engine running at wide open throttle. If it checks out start tracing the wiring harness for loose plugs or broken wires.

Check your stator and voltage regulator for proper output. Sounds like the battery isn't receiving a charge through the system. You can charge the battery with a trickle charger to verify the battery will take a charge outside the bikes charging system.

Hi and welcome to FixYa,

Your description indicates that the battery is not charging when the engine is running. This could be:

• faulty regulator;
• loose/corroded connector/terminals at the regulator;
• loose wire/terminal from the regulator to the battery + terminal;
• loose battery ground to chassis/harness;
• loose ground from regulator.

Check and correct based on the above.

Good luck and thank you for using FixYa.