I recently acquired a very large 12V SLA battery and want to make a UPS for my computer. I think I have the basic idea, but I'm not entirely sure how I would go about this. I'm guessing I could use a relay to switch from the mains to battery, but then I would need a very large capacitor to run the equipment for a few milliseconds whilst it switches. I would need a separate transformer and regulator for the relay, and also an inverter for the battery, which I will probably buy as it looks like it would be too hard to make. Is this the right approach to it?