The  primary  disadvantage  of  constant  current charging   is   that   THE   CHARGING   CURRENT REMAINS  AT  A  STEADY  VALUE  UNLESS  YOU CHANGE IT. A battery charged with too high current rate would overheat and damage the plates, making the battery useless. Do NOT allow the battery temperature to exceed 110° while charging. CONSTANT   VOLTAGE   CHARGING.— Constant  voltage  charging,  also  known  as  constant potential  charging,  is  usually  done  with  a  motor generator set. The motor drives a generator (similar to a   generator   on   a   vehicle);   this   generator   produces current to charge the battery. The voltage in this type of system  is  usually  held  constant.  With  a  constant voltage, the charging rate to a low battery will be high. But as the battery approaches full charge, the opposing voltage  of  the  battery  goes  up  so  it  more  strongly opposes  the  charging  current.  This  opposition  to  the charging  current  indicates  that  a  smaller  charge  is needed.  As  the  battery  approaches  full  charge,  the charging  voltage  decreases.  This  condition  decreases the ability to maintain a charging current to the battery. As a result, the charging current tapers off to a very low value  by  the  time  the  battery  is  fully  charged.  This principle of operation is the same as that of the voltage regulator on a vehicle. CHARGING   PRACTICES.—It     is     easy     to connect  the  battery  to  the  charger,  turn  the  charging current on, and, after a normal charging period, turn the charging  current  off  and  remove  the  battery.  Certain precautions however are necessary both BEFORE and DURING  the  charging  period.  These  practices  are  as follows: 1.   Clean and inspect the battery thoroughly before placing it on charge. Use a solution of baking soda  and  water  for  cleaning;  and  inspect  for cracks or breaks in the container. CAUTION Do not permit the soda and water solution to enter the cells. To do so would neutralize the acid within the electrolyte. 2.   Connect the battery to the charger. Be sure the battery   terminals   are   connected   properly; connect  positive  post  to  positive  (+)  terminal and the negative post to negative (-) terminal. The   positive   terminals   of   both   battery   and charger   are   marked;   those   unmarked   are negative. The positive post of the battery is, in 3. 4. 5. 6. 7. 8. most  cases,  slightly  larger  than  the  negative post. Ensure all connections are tight. See that the vent holes are clear and open. DO NOT  REMOVE  BATTERY  CARS  DURING CHARGING. This prevents acid from spraying onto the top of the battery and keeps dirt out of the cells. Check   the   electrolyte   level   before   charging begins  and  during  charging.  Add  distilled  water if the level of electrolyte is below the top of the plate. Keep  the  charging  room  well  ventilated.  DO NOT  SMOKE  NEAR  BATTERIES  BEING CHARGED.   Batteries   on   charge   release hydrogen  gas.  A  small  spark  may  cause  an explosion. Take frequent hydrometer readings of each cell and  record  them.  You  can  expect  the  specific gravity to rise during the charge. If it does not rise, remove the battery and dispose of it as per local hazardous material disposal instruction. Keep  close  watch  for  excessive  gassing, especially at the very beginning of the charge when   using   the   constant   voltage   method. Reduce   the   charging   current   if   excessive gassing  occurs.  Some  gassing  is  normal  and aids in remixing the electrolyte. Do  not  remove  a  battery  until  it  has  been completely charged. Placing New Batteries in Service New batteries may come to you full of electrolyte and fully charged. In this case, all that is necessary is to install the batteries properly in the piece of equipment. Most   batteries   shipped   to   NCF   units   are   received charged and dry. Charged and dry batteries will retain their state of full  charge  indefinitely  so  long  as  moisture  is  not allowed to enter the cells. Therefore, batteries should be stored in a dry place. Moisture and air entering the cells  will  allow  the  negative  plates  to  oxidize.  The oxidation causes the battery to lose its charge. To  activate  a  dry  battery,  remove  the  restrictors from the vents and remove the vent caps. Then fill all the cells to the proper level with electrolyte. The best results  are  obtained  when  the  temperature  of  the battery  and  electrolyte  is  within  the  range  of  60°F  to 80°F. 2-6