TM 11-6140-203-14-1
is low and must be adjusted using distilled water fol-
accumulates. If sufficient pressure builds up, the cell
lowing the procedure given in c below. Adjustment of
will rupture. The electrolyte may then flow over the
electrolyte level is not authorized at the organizational
top of the cells and down into the case bottom between
(AVUM) level.
the cells. The overflow of electrolyte eventually starts
NOTE
corrosion and may cause a short circuit between the
A low setting of the aircraft voltage regula-
cell connectors. This chain of events, particularly the
tor will result in the battery being only par-
accumulation of hydrogen, can lead to an explosion.
tially charged and therefore an apparent low
An igniting spark could be caused by a loose cell con-
level of electrolytes.
nection or a short circuit between the cell connectors
b. Adjusting Electrolyte Level. The electrolyte level
resulting from the spewed electrolyte. Electrolyte
of cells in a nickel-cadmium battery should not be ad-
(KOH) should only be added to a new cell on its initial
justed when the state of charge is unknown. The level
charge or if large amounts of electrolyte have spewed
of the electrolyte should be adjusted after the battery
out of a cell.
has been completely charged and allowed to rest for at
d. Check State of Charge. Before adjusting a sus-
least 30 minutes. The procedure is exactly the opposite
pected low electrolyte level, cycle the battery in the
of that for lead-acid batteries in which the electrolyte
shop to assure that it is fully charged. Conversely,
level is adjusted by adding water before placing the
never allow electrolyte to fall below the cell level indi-
battery on charge, or whenever the electrolyte level is
cators (if used) when the battery is in a charged condi-
low. An inherent characteristic of nickel-cadmium
tion. Low electrolyte levels in the charged condition
cells is that when they are in a low or discharged condi-
will cause the cells to heat up, resulting in their ulti-
tion, the electrolyte is absorbed within the plates and
mate destruction.
separators to a point where it is not visible from the
top of the cells. When the battery is recharged, the
tures
electrolyte level rises. At full charge, the electrolyte
level is at its maximum.
a. Nickel-cadmium batteries must be kept away
c. Adding Distilled Water or Electrolyte (KOH). If
from lead-acid batteries to avoid contamination.
distilled water or electrolyte (KOH) is added to nickel-
b. State of charge cannot be determined with a spe-
cadmium cells while the battery is in the aircraft or ve-
cific gravity check of electrolyte in nickel-cadmium
hicle and the state of charge is unknown, electrolyte
batteries.
may boil or spew through the filler caps as the battery
c. Adjust electrolyte level only when the nickel-cad-
receives its charge from the power bus. The potassium
mium battery is fully charged and allowed to rest for
hydroxide contained in the electrolyte may eventually
at least 30 minutes. If level is low, use only distilled
plug the vent valve of the filler caps. If the vent valves
water.
become plugged, pressure builds up in the cells and gas
