I have 2 18v dewalt batterie guns when i put the bateries on charge after a few mins they just flesh red and dont charge any ideas?

May read instructions and see if charger is compatible of charging the two types of batteries you are charging ,,,,I have 32 dewalt 18v dc9096 batteries and 1d dewalt 18v dc9099 battery

Depending on how old or more to the point how many times you have already charged the battery, it may be worn out. All rechargeable batteries do reach a point where they won't charge up anymore. If you have fully discharged the battery and tried to fully charge it up again and it won't take a charge or only lasts a few minutes on a charge it may be time to recycle it and buy a new one.

on the charger there is a red LED that blinks while it is charging when it is fully charged it will not blink usually about 1 hour to charge a DeWalt 18v battery

Take your battery to a Batteries Plus store and have them test it. I suspect you're going to need a new battery. That one is no longer taking a charge.

Is it Nano li-ion? have you got another spare battery to double- check?
I experienced the same problem with 18V Dewalt nano li-ion battery. Was fully charged, came to work- Dead!!! I was lucky I had spare one, so then i was ok, but anyways had to buy a new one. Check on these things:
1. Battery is faulty. If u have any chances to ask someone who has the same gun (voltage is very important!!! has to be the same!!!- 12V battery to 12V gun, 14.4 to 14.4, 18 to 18 etc). Put your battery into that other gun. If You find the same problem that means your battery is dead.
2.Gun with battery contacts. If you 100% sure, that batterIES (check 2 batteries, or more) are OK, check bottom contacts where u put battery in, use WD40, or similar to clean them.
3. Least common Dewalt thing (Most common in Panasonic drills) is trigger contacts.
Basically i do not know what model is your dewalt, i was only talking in general, but there are no miracles- stopped working suddenly, and what u describe new, for instance my new drill dw727kd is less than 1 year old, i was too stuppid to open that battery myself to void warranty :(
AAAAHHH!!!!!! One more thing - If you have not tried to open these screws- check your nearest Dewalt authorised repair center- new NANO batteries have 2year warranty!

the battery is bad, the fast flashing red indicated an internal short in the battery or it is consumed and needs to be replaced.

if it is under warranty ,take it back .if it isnot then bite the bullet and buy a new battery ----try TOOLKING

There are typically two to three contacts on battery packs. One to charge the battery, one to 120v (household) ground, and in the case of the third contact, grounding the battery pack.

Are batteries for the dewalt cordless drill interchangeable? Will an 18 volt battery fit in a 12 volt drill?

take it back to where you purchase and dont forget bring your receipt