I am building a flashlight using a large(ish) 35W HID headlamp from a car, and I'm having troubles choosing a good battery technology.
The inverter draws about 3.5A - 4A at 12V, tested on a large power supply. The current range I have supplied is through a Pb battery's discharge curve, from 12.5V to 10.5V. I have looked at purchasing a small 4Ah 12V Pb battery, but I am hesitant, because I am unsure of what currents the battery may be able to supply. I know the battery is small, but I have a small budget (Got the HID bulbs for free off a friend), and I am OK with a 30 minute battery life, as that is the max time I will be using it.
Any suggestions on what kind of discharge rate I could get from such a small Pb battery?