Strain the soaked kidney beans and add it to pressure cooker. For 1 cup of kidney beans add 3 cups of water. Close the cooker lid and pressure cook for good 4-5 whistles and then lower the heat to medium low to cook for another for 15-20 minutes. Allow the pressure to release naturally. If you want to boil rajma in pot, then add enough water and bring it to a boil. Then, add strained rajma and cook it for good 1 hour at least. It takes quite a long to boil rajma in pot. To boil kidney beans in Instant pot, add strained beans along with 2.5 cups of water and pressure cook on 'High' for 30 minutes. Let the pressure naturally.