I have a device that runs on 9V battery. It consumes about 100 mA @ 8.5 V. I am trying to replace 9V battery with rechargeable Li - ion battery (1 cell nominal 3.7 V). I have connected Li-ion battery to input of LT3580 (schematic attached). The circuit works fine when the load is not connected. The output of LT3580 is around 9.56 V. When I connect the load output voltage of LT3580 drops to battery voltage. According to data sheet this configuration should give me around 500 mA but I am not getting expected output.