When using a set of fresh alkaline cells, the combined voltage is 6V

I don't like Alkaline cells, for various reasons... but it needs to be noted, in a pinch any readily available drug store alkaline battery will work in this.

With 4 fresh Rayovac alkaline AA batteries, it wasn't able to charge my phone by more than 1 or 2 percent.

I suggest keeping a very large pack of reasonably good alkaline AAs at home or wherever you might need them, along with AA flashlights (Hausbell or UltraFire), plus this charger

When using a set of fresh alkaline cells, the combined voltage is 6V

So this charger works perfect as long as you use very strong batteries.

So this charger works perfect as long as you use very strong batteries.