I know you'll be looking at this product after you have bought it and thinking there is another part that comes with it... there is a battery caddy that you fit your battery into that then slips into the charger.
Red light tells you it's charging and the green light says it's charged.
Haven't tried it in the car, the charge holds for the same amount as the Nikon charger... that is lost!?!
What excites me is that if I can change the caddy for another Nikon camera battery, I'd have no need to pack 2 chargers on field trips. Looking into that just now and I will update when I know.
So short version, charges the battery, light indicator goes green when charged, takes the same amount of time as the Nikon charger and doesn't feel hot if you leave it charging overnight. Conclusion... good buy!