You're thinking of cars, industry and others that have high value batteries.
Power tools, smartphones etc charge to the maximum 4.2V/cell, sometimes even 4.3V (some chemistries safely allow it) because the average person just wants the maximum runtime and will replace the equipment before the battery degrades significantly.
A cow also produces a lot of methane, a much worse greenhouse gas.
Besides, the problem isn't the grass from cows grazing, it's the rainforests that go down all around the world to convert to farmland to produce animal feed.
It's much more efficient to use that farmland to feed humans than to feed cows and then feed humans (1kg of meat needs 25kg of feed)
Disclaimer - I'm not vegan but I try to reduce my meat consumption overall, especially red meats.