Ntn7143cr battery won,t charge. put in charger flashes red then green.

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.

Batteries don't always look degraded but if they've been in use for a while or have a bad cell, they will show up bad on the charger and it won't charge them. The only way to test the batteries is to try to charge them on another charger. If the batteries show defective on another charger, they are bad and you'll have to replace them. Also try to charge some batteries you know to be good on your charger to see if it's the problem. If your batteries charge on another charger, your current charger is bad and they don't have any replaceable parts in them so you'd be looking at replacing it.

The battery is gone for sure... You must get new one... take a look on amazon (my recommendation): Amazon com nailers paslode battery

If you put a battery on your charger and both red and green lights flash it is indicating that battery is defective. There may be a short in the battery or they just may be too old and worn out to charge anymore. If the charger is reading the battery as defective it will not charge the battery. The only fix is to buy new batteries.

Ridgid charger lights read as follows: Solid red; charger has power. Flashing red; charger is evaluating the battery, checking if it's cool enough to charge and if it is in chargeable condition. If the battery is hot, i.e. just came off the tool after extended use, it won't charge the battery until it cools down. Flashing red & green; the battery is defective and the charger will not charge it. Solid red & flashing green; battery is charging. Solid green; battery is full.

I had the same problem with flashing red lights. Both sides on a four battery charger. I swapped the batteries to another charger and the batteries were fine. They charged normally. I put some different batteries in the charger and the same flashing light situation. Those batteries also charged normally in a different charger. I looked closely at the back of the charger and, low and behold, "made in China". Why does that not surprise me. The bottom line, it may not be a battery issue.

Yep, not the batteries, mine is doing the same thing but my second charger works fine with the same batteries

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.

sounds like a dead battery. Plug the origional charger into it and the front led (below the flash) should flash red. If the red led in the back of the camera flashes or stays lit, then you have the wrong charger plugged in. (the camera won't power up if the back red/green led is on when plugged in)

the charger in the laptop is not functioning. pc will need repaired