l.e.d light

Read this and then come back with any questions you have.

 

You might be right.

Some form of current limiting is *essential*

 

If that is the device you are using, then it has resistors incorporated in it and can operate from a specified voltage.

Otherwise, you need to determine the following:

a) LED forward voltage drop (or sum of these if you connect several in series)
b) LED current
c) Power supply voltage

Add from these calculate the series resistor value.

(a) and (b) are typically specified for a device, often in terms of a graph showing one vs. the other. You will want to choose a LED current less than the maximum, and use this to determine the forward voltage drop.

You have already told us that (c) is 12V

If you don't have specs for the LEDs then there are some rough figures for forward voltage drop in the article I pointed you to.

 

Yes, your circuit determines the current. Your choice of battery should be based on current, discharge characteristics, capacity, weight, size, required run time, etc.

The 7Ah battery has just over five times the capacity of the 1.3Ah nicad pack. You can find the approximate run time by dividing the Ah rating by the current in amps.

So if your strings of LEDs draw 120mA (0.12A) then the 7Ah battery will last 7/0.12 = 58 hours and the nicad pack would last just under 11 hours. However it is generally considered poor form to discharge a lead acid battery below 50% on a routine basis, so 28 hours for the lead acid battery vs, 10 for the nicad pack are more reasonable figures.

Of course these figures are based on a totally made up current draw that almost certainly does not correspond with what you have. You should repeat the calculations with your actual figures.

It may also be a good idea to show me how you plan on connecting the LEDs so that I can double-check that you have everything correct.