Are you using a genuine Olympus BLM-1 or a cheap "compatible" battery. It's possible that the original fault was caused by a worn out battery, but if you've bought a cheap compatible from places like eBay or Amazon then they're often very poor quality and frequently not of the stated charge capacity. Sometimes they're not even lithium batteries so your charger and camera won't work properly with them They're often so cheap that there is no effective quality control so your new battery may well be a faulty one. There is no way that the new battery would have been fully charged after just eight minutes: although they're usually supplied with a partial charge it's nowhere near a full charge.

Another possibility is that your Olympus BCM-2 charger is faulty.

Worst of all, you may simply have been sold a pup. If the eBay seller described the camera as being in good working order then I suggest you ask for a refund and return the camera. Although private sales are "as seen" they also have to meet the sellers description. If the seller won't play ball then you may be able to claim PayPal buyer protection if you used it to pay the seller.

Your camera is a five year old model now and way outside the warranty, in the UK perfectly good used examples sell for around £125 and this is likely to be less than the likely cost of any repairs if you send it to Olympus. You'll need to carefully weigh up what you've paid so far, what you're likely to have to additionally buy just to diagnose the fault correctly and what you can get if you just cut your losses and sell the camera as is.