2.  Discharge rate (high current rates yield less capacity  than low rates). 3.  Temperature (capacity and voltage levels decrease  as battery temperature moves away from the 60 °F  (16 °C) to 90 °F (32 °C) range toward the high and  low extremes). 4.  Charge rate (higher charge rates generally yield greater  capacity). Aircraft Battery Ratings by Specification Temperature Correction Storing and Servicing Facilities Battery Freezing 9-23 Figure 9-37.  Sulfuric acid temperature correction. Figure 9-36.  Lead-acid battery electrolyte freezing points. NOTE: Only a load check determines overall battery condition. The one-hour rate is the rate of discharge a battery can endure  for 1 hour with the battery voltage at or above 1.67 volts per  cell, or 20 volts for a 24-volt lead-acid battery, or 10 volts for  a 12-volt lead-acid battery. The one-hour capacity, measured  in ampere hours (Ah), is the product of the discharge rate and  time (in hours) to the specified end voltage.  The emergency rate is the total essential load, measured in  amperes, required to support the essential bus for 30 minutes.  This is the rate of discharge a battery can endure for 30  minutes with the battery voltage at or above 1.67 volts per  cell, or 20 volts for a 24 volt lead-acid battery, or 10 volts  for a 12 volt lead-acid battery. Separate facilities for storing and/or servicing flooded  electrolyte lead-acid and NiCd batteries must be maintained.  Introduction of acid electrolyte into alkaline electrolyte  causes permanent damage to vented (flooded electrolyte)  NiCd batteries and vice versa. However, batteries that are  sealed can be charged and capacity checked in the same area.  Because the electrolyte in a valve-regulated lead-acid battery  is absorbed in the separators and porous plates, it cannot  contaminate a NiCd battery even when they are serviced in  the same area. WARNING: It is extremely dangerous to store or service  lead-acid and NiCd batteries in the same area. Introduction  of acid electrolytes into alkaline electrolyte destroys the  NiCd, and vice versa. Discharged lead-acid batteries exposed to cold temperatures  are subject to plate damage due to freezing of the electrolyte.  To prevent freezing damage, maintain each cell’s specific  gravity at 1.275 or, for sealed lead-acid batteries, check  open circuit voltage.  [Figure 9-36]  NiCd battery electrolyte  is not as susceptible to freezing because no appreciable  chemical change takes place between the charged and  discharged states. However, the electrolyte freezes at  approximately –75 °F. U.S.-manufactured lead-acid batteries are considered fully  charged when the specific gravity reading is between 1.275  and 1.300. A  1 ⁄ 3 discharged battery reads about 1.240 and  a  2 ⁄ 3 discharged battery shows a specific gravity reading of  about 1.200 when tested by a hydrometer at an electrolyte  temperature of 80 °F. However, to determine precise specific  gravity readings, a temperature correction should be applied  to the hydrometer indication.  [Figure 9-37]  As an example,  for a hydrometer reading of 1.260 and electrolyte temperature  of 40 °F, the corrected specific gravity reading of the  electrolyte is 1.244. Electrolyte Temperature  °C +60 +55 +49 +43 +38 +33 +27 +23 +15 +10 +05 –02 –07 –13 –18 –23 –28 –35  °F +140 +130 +120 +110 +100 +90 +80 +70 +60 +50 +40 +30 +20 +10 0 –10 –20 –30 Points to Subtract From or Add to Specific Gravity Readings 12 volt +0.024 +0.020 +0.016 +0.012 +0.008 +0.004  0 –0.004 –0.008 –0.012 –0.016 –0.020 –0.024 –0.028 –0.032 –0.036 –0.040 –0.044 Freezing  Point Specific Gravity 1.300 1.275 1.250 1.225 1.200 1.175 1.150 1.125 1.100  °C –70 –62 –52 –37 –26 –20 –15 –10 –08  °F –95 –80 –62 –35 –16 –04 +05 +13 +19 State of Charge (SOC) for Sealed Lead-Acid Batteries at 70° SOC  100% 75% 50% 25% 12 volt 12.9 12.7 12.4 12.0 24 volt 25.8 25.4 24.8 24.0