If you can afford to spend a little more, the cheapest I know of that has VW is the Innokin VV v3.0. It's a cracking battery, similar size to an ego, but the benefit of VW, which is such an improvement on fixed or just VV.
Also, you can use it while charging, so if you're well organised or usually near a power supply, you could just about get away with just one (though personally, I always think one should have spares)
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