Battery concern Rayovac (NYSE:ROV) plans on acquiring Germany's Tetra. If this sounds a little strange, maybe that's because it is, kind of. (Meanwhile, if the name "Tetra" sounds like something that belongs alongside your aquarium, that's because it is.) The battery maker is diversifying into pet products.

Tetra focuses on fish. Indeed, there is such a thing as an electric yellow cichlid, which is a guy that swims around an aquarium. There are also electric eels, which of course, one probably wouldn't want as a pet. None of these options require batteries, of course. (End rather strange exercise in trying to connect batteries and pets. Point is, it's just hard to do.)

The acquisition might not come as a surprise to those who have been following Rayovac, considering it recently purchased another company with assets of the pet persuasion, United Industries Corp., which also provides lawn and garden supplies, as well as pet paraphernalia.

In terms of the logic behind expanding into the pet supply business, one might not look any further than one of the recent Motley Fool Stock Advisor picks, PETsMART (NASDAQ:PETM). It's clear that there's money in pets. After all, it's a $34 billion industry, according to the American Pet Products Manufacturers Association, and modern families are more likely to see pets as a part of the family than ever before. (How many people do you know who only half joke that their pet is their "child"? Probably several.)

Of course, Tetra focuses on "ornamental fish keeping" -- and some reptile gear -- although one might imagine this wouldn't garner as much growth as stuff for dogs, cats, and other fuzzy friends, which often need tons of food, accessories, toys, litter, and so forth.

Ultimately, though, one might consider Peter Lynch's advice about "deworseification" in what many Fools consider required reading, One Up on Wall Street. That's when companies lose their primary focus in their quest to jumpstart growth through diversification. Of course, this is hardly unheard of in the battery biz. The other names in batteries, like Gillette (NYSE:G) and Energizer (NYSE:ENR), have also pulled other consumer products under their umbrellas, most notably razors and blades (an area in which Rayovac also competes).

Rayovac will change its name to Spectrum Brands, and it will pay up $551 million for Tetra, which has annual sales of $267.5 million. Investors bid shares of Rayovac up almost 10% yesterday on the news. It remains to be seen if such optimism will end up seeming a bit fishy.

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Alyce Lomax does not own shares of any of the companies mentioned.