For me, on the iPhone and iPad Pro that I use: I'd personally prefer 600g less, since the battery already lasts absurdly long for my uses and I'm rarely without a charger. But double the battery life for just 600g is a crazy good tradeoff, so I wouldn't begrudge anyone for making that deal. If Tim Cook came out and said the next iPhone/iPad was going to be 600g heavier but with double the battery life, I wouldn't be upset at all.