BATTERY Figure 7 illustrates the correction for hydrometer readings when the acid temperature is above or below 26.7^oC (80^oF).  In example No.  1, in cold weather, a partially discharged battery in a vehicle at 6.7°C (+ 20°F) might read 1.250 indicating it was almost fully charged. However, when the correction factor is applied, the true value is only 1.226.  Example No.  2 could be encountered in a battery exposed to the sun In hot weather.  Also, electrolyte frequently reaches 43°C (1000F) in service in warm weather.  The 1.235 specific gravity reading might indicate too low a state of charge to install in a vehicle or that there is a problem in the electrical system if the battery is in service.  However, the true reading of 1.246 may not be unreasonably low depending on the length of storage of the battery or the type of service which it has been experiencing in the vehicle. MT-23241 Figure 7 - Specific Gravity Temperature Correction Valves SPECIFIC GRAVITY DETERMINES ELECTROLYTE FREEZING POINT Specific gravity of the electrolyte determines the temperature at which a battery will be harmed or damaged by freezing.  A fully charged battery can be stored at sub-freezing temperatures without freezing the electrolyte.  However, as a battery approaches the discharged condition, the electrolyte will freeze at higher temperatures.  Table 2 shows the approximate freezing points of electrolyte at various specific gravities. TABLE 2 Specific State of Freezing Gavity Charge Point 1.265 100% -59.5°C (-75°F) 1.225 75% -37.2°C (-35°F) 1.190 50% -26.1°C (-15°F) 1.155 25% -15.0°C (+15°F) 1.120 Discharged -  9.4°C (+15°F) Batteries must be kept fully charged when batteries or vehicles are stored in sub-freezing temperatures. TEMPERATURE AFFECTS BATTERY OUTPUT CAPACITY (CRANKING POWER) Battery temperature affects the output capacity of a battery with respect to cranking an engine.  The cranking power of the battery is reduced as battery temperature is lowered. Table 3 lists the approximate percentage of output capacity of a fully charged battery at various temperatures. Note that a fully charged battery at - 17.8°C (0°F) gives only 40 percent of its cranking power at 26.7°C (800F). TABLE 3 Percentage of Battery Temperature Capacity (Fully Charged) 26.70C (80°F) 100% 0°C (32°F) 65% -17.8°C (0°F) 40% -28.8°C (-20°F) 20% Batteries at less than the fully charged state will provide even less of their output capacity.  This emphasizes the importance of keeping vehicle batteries fully charged when low temperatures will be encountered. MAINTENANCE (IN VEHICLE) The battery is a perishable item and requires attention. With a reasonable amount of care the life of a battery can be appreciably extended.  Neglect and abuse will invariably cause shorter battery service life. The battery should be inspected at the time of chassis lubrication or other periodic services. Battery maintenance includes the following: 1. Inspect battery and mounting (Figure 8). 2. If corrosion is found on the terminal posts, remove the cable terminals from the battery (ground cable first) using the proper end wrench and a cable puller. A terminal cleaning brush can be used to clean tapered posts and the mating surfaces of the CTS-4111B - Page 7