When charging battery flashes red then stays on red.how long should it take to change to green?.its a dewault9130 18 volt

If it flashes 7 green and one red for the 8 total then it's a joystick error. If it's 8 green and one red then it is a control/brain error code. Measure voltage on batteries when turn chair on. Both batteries need to stay above 11.5 volts each.

If it changes from red to green and stays green while being charged, it is just a sign that it is being charged and there is nothing wrong.
If it flashes back and forth between red and green while charging, there might be something wrong with your charger's connection.

Should use proper 24 volt 2-4 amp off-board charger. A 3 red, 3 green flash code on a VSI/Remote Plus controller indicates high battery voltage.

according to manualslib type site for the wg540, solid red means charging for the wa3840 and wa3838. After 30 minutes if battery has not reached 10 volts (of 18), the red will begin flashing meaning defective.
Just green? Ready to go. Green flashing? Overheat.
Tangent; sometimes a discharged battery needs a little coaxing - have to get a little voltage into the battery for charger to try to charge. Different company, electric drill. I plead ignorance if this applies for the 3840 since they mention the half an hour time.

Phil after a full charge you should be reading more than 24.8 volts on the batteries I'm still leaning toward replacing the batteries of course thats not cheap but if you can locate 2 batteries from a provider that will let you try them on the scooter to see if that fixes the flashes you are getting I don't have too many more ideas to give you sorry

When the charger light is changing from red to green that is a indication that it is charging the battery. When the charge is complete the light will stay green until the battery is removed or the charger is unplugged.

Dust getting in the charger is a problem, Try blowing it out with a moisture-free dust remover, found at most any store. Green flashing means improper power, due to dust or power from the outlet, try a differant wall outlet. Red flashing means the charger or battery is to hot and must cool down before it will charge. The charger will not charge a battery if the lights are flashing. Solid Red light means it is charging and solid green light means it is charged. Plug the charger in first before putting the battery on the charger. If the charger has been droped or hit the floor the coil inside could have broke loose and dammaged the charger requiring it to be replaced.

I hooked a 12 volt car battery charger to the battery for about two min. Then I put it in it's own charger,the yellow & green lights came on for about 5 sec. then the red light came on . About 30 min. later the green light came on and the battery is fine.

Hello,
Here's a copy from the owners manual:
■ Charging LED 
Red LED is on = Being charged 
Red LED is blinking = Charging error 
Green LED is on = Carging is complete


● If the charge indicator blinks as red, it indicates a battery charging error.
- The battery is not properly inserted
- The terminals of battery are dirty or damaged
If the battery is inserted properly and the charge indicator continues to blink, contact the
nearest Samsung Camera Service Center.


Another charging error is when the batteries are so depleted, they won't charge up to 100% anymore = red light doesn't go out and remains on for too long, means get a new battery.