Can i charge a 18volt ryobi battery on a 14.4volt charger

SOURCE: can i charge a 14v battery using a 18v charger (both are ryobi)

Absolutely not. The risk of damage to the battery is only a minor concern compared to the fire hazard you would be creating.

SOURCE: light on ryobi 18v charger

More than likely a defective battery sinse the other ones charge fine..
Bring it back for exchange of another one..

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SOURCE: Ryobi p111 charger -- light stays red

My charger do the same thing. I talked with the service people at Ryobi who said that the red led never goes out no matter how long you charge it. They suggested just charge it for 12 hours and then disconnect. Pretty dumb system, but that's apparently the way it is.

SOURCE: Will the ryobi nicad charger also charge the

No, but the Lithium charger will charge the NiCads.

SOURCE: can you charge ryobi lithium batteries in a

NO! Never charge lithium batteries in a charger designed for nickle based batteries like the NiHi your old charger was meant for. Ryobi did design the new Lithium charger to be backwards compatible so you can charge your older 18V NiHi batteries in the Lithium 18V charger.
Also note, NEVER miss-match the voltage, for example, make sure you are not trying to charge 12V batteries in an 18V charger unless the manufacturer has specifically stated that the charger is capable of multiple voltages.