I have a 12 volt Ni Cad Screwdriver battery (to be exact, it is a Black & Decker Firestorm) I would like to find the amp-hours of the battery. The battery doesn't say anything on it (except that it is 12 volts), and I couldn't find any info online. I have no amp meter for testing amps drawn/time, but I tested a 12 volt 21/5 watt bulb and it lasted around 45 minutes. I did the division of (21/5)/12 and got .35 amp hours if it lasted an hour, but it was only 45 minutes and that would be less than .3 amp hours. I don't think this is true. So am I doing anything wrong and if so, what should I fix, and how can I find the amp hours?
edit: The model number of the pack is ps160 12v type 3 power pack
edit 2: I just figured out that the 21/5 means there is 2 filaments and doesn't mean "21 divided by 2" so I probably used the 21 watt because I used the brighter one.