I think some do. I don't use my macbook anymore so don't have it on hand to check, but both my HP laptops (one running windows, the other linux) and my iphone s

I think some do. I don't use my macbook anymore so don't have it on hand to check, but both my HP laptops (one running windows, the other linux) and my iphone seem to not fluctuate the battery charge if I leave them plugged in. The iphone doesn't even get warm, which can happen when it recharges from a drained battery. The laptops won't even attempt to charge if the battery's above a certain threshold, like 95%. My linux laptop barely moves from my desk, so it regularly spends multiple days on end with the battery showing something like 96%.