Not bad! I love it when I find that kind of stuff lying around!
depending on the age of the batteries, they might not have 12ah capacity anymore, but still, free is hard to argue with.
One more thing, you might check to see if you can use them in parallel, which would give you 24ah. In parallel means you connect both batteries + posts together, and both - posts together. BE SURE to do it this way. Connecting the + on one of the batteries to the - on the other is running in series, which will double your voltage, which will quickly burn out your lights. Running in parallel will keep it at 12V - which is where you want it.
one word of warning though, the battery will only be as powerful as the weakest cell. lead batteries generally have 6 cells, and if one is bad, that one cell will discharge all the other cells. That said, if you have 2 lead batteries running in parallel, and one of the cells is bad, it will actually discarge itself and the other battery. Running two batteries in parallel effectivly double the chance of a failure since now you have 12 cells that have to be maintained.
In other words, it's not good to run batteries in parallel unless they are exactly the same, and have been used for the same application for their entire life. An example is a UPS battery (UPS meaning thoes heavy things that run comptuers when the power goes out). Some of the bigger units use multiple batteries in parallel, so if thats how these batteries were used, you are probably safe running them in parallel also.
one way I know of to test to see if the batteries are compatible with running in parallel is to do this. Hook both negative terminals together on the battery, then use a multimeter set to amps, and connect both terminals of the multimeter to the + posts on the battery and see if any current flows through. If the meter reads 0, you're okay, however if the meter says anything, even + or - .01 for longer than a few seconds, then you know one of the batteries is pulling current from the other, and will eventually discharge the cells.
If you can't tell by now, I'm partially a battery nerd
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