I have some old led strip that I want to use for light when camping. Not sure what you call it but it is white and only has the power wires, so it's either on or off. I want to run it off a battery and was trying to work out how long a battery would last. I'm assuming I measure the current going to the strip. I then divide the Ah rating of the battery by this amount to get the number of hours it will last in theory. Then some sort of allowance would need to be made as you don't want to take a battery to dead flat. Is this the correct process or are there other rules of thumb (eg in real terms the battery is only good for half the Ah rating or something like that).