I have a 12v / 5A battery nobreak gel that I already left connected with a 1N5402 + diode one bulb in series to the battery terminals for a few hours but the battery is not holding the charge. Is there any method to save or recover the battery?

What is the battery age? If more than 5 years, then it will not help her any more. For normal charging, you should use normal chargers. Purchased or homemade.