I think I've posted this before somewhere, but it's pertinent to this discussion too. I bought a £15 'Cree' 4.5v light from
Ebay and whilst the light itself was (and continues to be) wonderful, the battery-pack was awful. I took it apart and found two dummy batteries (carefully disguised as real ones) and two old batteries that were probably reclaimed from old laptops (one of which didn't make contact properly). So
one usable (if reclaimed) battery out of four! All batteries had been re heat-shrunk, so looked brand-new until that was removed.
Since I'm handy with a soldering iron, I was able to make up a replacement battery-pack using two old Nokia mobile phone batteries run in parallel. In this form, the setup has given faultless service all through winter, and doubled-up as a bedside table lamp!
There was nothing
dangerous about the battery-pack I received, but I do wonder how many people are out there using battery-packs with dummy batteries in them (since most aren't as inclined as I am to take electrical things apart).
I like the 4.5v front light, BTW, because it allows me to use the same charger for both front
and rear lights, and avoids the battery 'balancing' problem that can occur when batteries are recharged in series.