Battery Depleted

Like many others I also seem to have a problem with the camera (Optio S30 bought 18 months ago) telling me that my batteries are depleted. That isn't the case.! I've tried many other batteries (re-chargeable and non re-chargeable). Sometimes the camera works for 20-30 pictures (and more) whereas other times I can't get it to stay switched on. I recently bought a battery tester and can confirm that all the batteries are at least in a good state. Is this a known problem with the Optio range? I've got an old Olympus which even though it's a lot larger than the Optio, I'm tempted to resurrect for its reliability.