Number is definitely a date code. Marked ratings do point to a battery though, maybe just an unconventional package? Perhaps a super cap? No Farad rating printed on it so I'm not sure that idea floats either though.
Definitely Lithium. But I can't read the entire marking on it. Does look like a cap though. Like Tony said, the positive marking is not consistent with electrolytic capacitors. First time I've ever heard of a Li-Cap. But then again I'm not well versed in all things electronic.
Apparantly that's what some are calling super caps. However I have found some somewhat conflicting information. Some say a SuperCap is basically just a capacitor with the cathode of a lithium battery, but some state it is indeed a battery+cap hybrid. I don't know, maybe no difference between the two. Without a Farad rating printed on it though, I think Irving may have nailed it.