alt Hacker NewsNiMH cells are like $1 each. Seriously, Amazon.com is quoting me $18 for 16 cells, AA Amazon Basics NiMH.
As I said earlier: it's likely a better strategy to buy 4 extra cells and keep them pre charged / topped off, rather than spending a few dollars on a better charger.
I'm not sure that's true in practice. Chargers are often shared in a household and you may not have control over people putting things back on the charger. My preference is to have something that charges more quickly, rather than a bunch of spare batteries.
Plus if you leave batteries on the overcharge-style charger for long periods of time, I'm pretty sure they just dissipate the extra charge as heat, and that charge is applied indefinitely. They essentially turn into little electric space heaters, sending that energy down the drain.