Unless you have a bunch of those solar cells from the garden lights already, I'd suggest looking into some that are more productive. Even 40 would take a week or so to charge a small SLA from a UPS (7 Ah). I've got several of those 1.8 Watt panels mentioned earlier, and they don't provide much useful power. I've got a 5 watt panel that does a fair job keeping a 12 Ah battery charged, but sometimes takes a few days if the weather isn't clear.
I kind of started playing with solar, much like you are now. A 100 watt inverter, will light a 14 watt CFL bulb about 6 hours, off the 12 Ah battery. Those small inverters are dirt cheap (under $10).
Would also look into a charge controller, have seen several over the years, under $20. It protects you battery from being over charged, or over discharged. Also have the diodes built in, to prevent night discharge through the panels. Batteries are expensive, but will last quite a while if you treat them kindly. The circuits I've seen, are kind of complex, and likely to cost about the same as off the shelf. Depends on if you are in it for the challenge.