Manual for black and decker electromate 400 What do lights two red and one blinking green indicate?

it's not a computer is this,
this tool is for cars, battery charge and jump. 11 years old
read page 6
https://www.manualslib.com/manual/16290/Black-And-Decker-Electromate-90556511.html?page=6#manual

this old toll has and old AGM battery inside
none made last this long ever, and if not kept then internal battery charged it will go bad in 6 months due to sulfation. !

here is a link to the instructions that came with your jump box:
https://www.manualslib.com/manual/17003/Black-And-Decker-Electromate-Vec027bd.html?page=4#manual

Most likely the battery in your device is worn out , This can happen a number of ways depending upon the type of battery . Standard lead acid batteries as used in automobiles fail this way when they are discharged completely too many times . Lithium and some other types of batteries can be sensitive to being left on the charger too long or NOt being discharged completely before being charged . In any case you need new batteries

According to the manual:
http://servicenet.blackanddecker.com/documents/English/Instruction%20Manual/90556511,VEC026BD.pdf
http://servicenet.blackanddecker.com/documents/English/Instruction%20Manual/90556511,VEC026BD.pdf
Red LED's indicate a low battery charge. I doubt with 2 Red, would start your car.

contact Black and decker i am sure they have some.

This link just might work for you: http://servicenet.blackanddecker.com/documents/English/Instruction%20Manual/90556511,VEC026BD.pdf

Fix expedtion

Why does the AC indicator light constantly flash and I have no AC power on my Black and Decker Electormate 400

I assume that your charger work fain and suggest to change your battery cause its seem that its gone.

I work for Black and Decker customer support. Our customer service phone number is 1-800-544-6986.

Please call the number above so that we can assist you with your part request.

While this doesn't actually solve your problem, I hope the information allows you to make an informed decision as to how to proceed from here. Please let me know if I can be of further assistance.