I think these have basically always been carbon-zinc, or alkaline.

Technically, zinc is a heavy metal, but basically harmless to humans unless you eat the whole thing. Alkaline batteries contain managous oxide, which is a heavy metal, but you’d need some serious chronic exposure to get into trouble from that.

It’s still a good idea not to open random crap that washes ashore, because there are definitely FAR more dangerous things that come in small metal cylinders. Like unexploded ordnance.