Wednesday, May 29, 2013

What Are Battery Capacity Ratings And How Battery Ratings Are Used?

One common battery rating is Amp-Hour (ah): Amp-hour rating for battery capacity is calculated by multiplying the current (in amperes) by time (hours) the current is drawn. Amp-hour battery rating is commonly used on sealed lead acid batteries. For example: A battery which delivers 2 amperes for 20 hours would have a 40 amp-hour battery rating (2 x 20= 40). Smaller batteries such as two way radio NiCad or NiMH are rated in mili-amp hours (mAh). 
Cold Cranking Amperage battery rating: CCA is the discharge load in amps which a battery can sustain for 30 seconds at 0 degrees F. and not fall below 1.2 volts per cell (i.e. 7.2 volts for a 12 volt battery). This battery rating measures a burst of energy that a car needs to start on a cold morning. This rating is used mainly for rating batteries for engine starting capacity and does not apply to NiCad batteries, NiMH batteries or Alkaline batteries. 
Reserve capacity battery rating: RC is the number of minutes a new, fully charged battery at 80 degrees F. will sustain a discharge load of 25 amps to a cut-off voltage of 1.75 volts per cell (i.e. 10.5 volts for a 12 volt battery). This battery rating measures more of a continuous load on the battery.

Peukert's law (wikapedia)