I have an emergency lamp consisting of 120 white leds that is connected to the mains 220vac. The battery inside is a sealed lead acid battery 6v 2.8ah. The lamp no longer works and the battery voltage now reads 4.45v. There is a switch by means of which either 60 leds or 120 leds can be lit. As the cost of a replacement battery is almost that of a new emergency lamp I would like to build a Joule thief circuit to run off the remaining voltage and current in the sealed battery. I would appreciate any practical advice concerning winding the ferrite toroid and current limiting resistors.