Checking my math

Just a tiny little post:

I just saw an ad for a powerful flashlight. The ad said the flashlight had a 55 watt bulb and a rechargeable 3 amp-hour 6 volt battery.

By my calculations, that means that the flashlight should run just under 20 minutes on a fully charged battery.

Am I missing something? Have the formulas changed?

Comments, if any, welcome.

2 Responses to “Checking my math”

  1. Kate W says:

    Is there something odd here with Amp-hours versus amps? That’s all I can think of but I am lacking in brain at the moment, and I got 20 minutes as well.

  2. waltcrawford says:

    I don’t believe so: Ampere-hours are a fairly standard way of measuring battery capacity, and as far as I know one ampere-hour at 6 volts is 6 watt-hours. So your 20 minutes agrees with my 20 minutes…