Ok here's the deal on that charger:
- the 15 min time is only for when you use the special batteries that came with it
- These special batteries have a low internal resistance to allow super-fast charging. As a trade-off, you also get faster-than-normal "self discharge" rates. This is the rate that the battery will lose charge on its own, even when not powering a device.
- the insanely-fast charging is done by using higher charge voltages than most chargers. This stresses the batteries more and can lead to premature failure. Most likely the flashing lights are due to bad batteries.
- This rapid charging also causes the batteries to get hotter than normal chargers, which also shortens the cell life. The temps get even higher if you charge batteries that are already mostly-charged.
In short, this may charge some batteries in 15 mins but there's a price to pay. You're going to be buying new replacement rechargables that have to be Energizer batteries far more-often than you would otherwise. How convenient for Energizer, hmm? No wonder they put this sketchy product on the market.