Have just got the Dewalt DE9116 charger.Plugged it in & red light comes on & then goes off.Is the charger working properly?Have no instructions

some batteries are bad from factory, you should exchange it for another and try again. Make sure the battery voltage and type (ie. lithium, Nickel Cadmium,etc.) match the charger. If not, you can buy most replacement batteries for older models on the internet. If a second battery doesn't work - it's the charger .

If this is a newer purchase, my newer Milwaukee flashes slow for the first two beats and then quickly while it reads the battery type and then shifts to the slow flashing charge light after it determines the type. this is because it is a smart-charger and can charge different types of batteries

Most likely it's the battery.
If you can find someone else with the same system then maybe they could check it for you. Unfortunately, you have the 20 volt system which isn't nearly as common as the 18V.
Or you could bring it to someplace like Batteries + Bulbs (If you have them around you) and they will tell you what's not working.

D23 is a transient voltage suppressor. Code: 1.5KE51A

IF is doing that without battery on it maybe charger is bad but if flashing that way when you put the battery could be the battery hope this helps!

If you plug the charger into the wall, turn on the power switch and the light comes on, the charger should be working properly. Here is a way to test it-
Attach the charger that came with the power chair to the power chair controller firmly and turn the power chair on, while the charger is running. What should happen:the lights on the controller will scroll back and forth. If this does NOT happen and you can confirm the charger is turned on, the charger handle is fully seated inside the controller receptacle and the wall outlet has power, then the charger may have a problem and needs to be replaced.

If the charger is OK, then there may be a problem with the batteries. Here are some sypmtoms:
1-You connect the charger but the light on the charger never goes red, it just stays green.
2-You connect the charger but the light goes from red to green VERY fast.
3-The charger light goes from red to green but when you disconnect the charger and press the power button on the controller, you only have one flashing red light, or the batteries drain within just a few minutes of use.
4-The power chair has been stored or sitting idle for several months.
5- The power chair has been connected to the charger 24-7 for several months.
Any of the above examples indicates that the batteries are oxidized or damaged and will most likely need to be replaced. The MPV5 takes two, U1 12 volt 33 amp batteries which can be purchased at any battery warehouse store like Interstate Batteries or Batteries Plus.
Good luck!

check output voltage on charger label most chargers are not regulated so if it says 18 volt output it may put out 24 volts but if its putting out 51 volts it may have a short batteries will get warm but not hot replace charger

I would say tee charger is no good. The only internal component is a circuit board so it is not worth trying to repair it/get spares as it will cost the same as replacing the charger.

when charger is plug in to ac it will blink once.normal voltage out for the unit in between 36v to 55 volt. the reading u have is normal.

sorry unit are non repairable. not even a wiring diagram for it.