Chemical Action of Discharge

TM 10-3930-644-14 & P

1. Chemical Action of Discharge

ness or damage when the battery is received. If

visual inspection of the carton indicates possible

When a cell is discharged by completing an

damage to the battery during transit or storage,

external circuit, the sulphuric acid acts on both

it should be opened and the battery carefully

positive and negative plate active material to

checked.

form the chemical compound lead sulphate.

The sulphate is supplied by the acid solution

4. Care of Stock Batteries in Original Equipment

(electrolyte)

which

becomes

weaker

concentration as the discharge proceeds. The

Batteries normally leave the manufacturing plant

amount of acid consumed is in direct proportion

in good condition, but excessive temperature

to the amount of electricity used from the cell.

and unusual vibration or jolts over long hauls by

When the acid in the electrolyte is partially used

trucks or railroads might affect the condition of

up by combining with the plates, the battery is

the battery. Always inspect for damage when a

said to be discharged. This gradual weakening

shipment arrives. Check batteries for possible

of the electrolyte in proportion to the electricity

cracks or damage and check cell readings with a

delivered is a very useful action because with

hydrometer. If not fully charged, recharge and if

the use of a hydrometer it can be determined

breakage has occurred, file your claim with the

how much unused acid remains with the water in

carrier.

the electrolyte, thus it can be judged how much

electrical energy is left in the cell.

Although many makes of batteries can

discharge quite rapidly while standing idle,

2. Chemical Action of Charge

especially in warm weather, Allis-Chalmers

batteries

are

built

with

exclusive

By passing electric current through the battery in

manufacturing process which reduces self-

a direction opposite to that of the discharge, the

discharge of wet batteries to a minimum.

lead sulphate is decomposed. The sulphate is

Normally, no care will be required unless the

expelled from the plates and returns to the

battery remains in stock for unusually long

electrolyte, thereby gradually restoring it to its

periods of time. However, it is recommended

original strength. This action frees the plate

that the battery be inspected every 30 days and

active materials of sulphate and they are

when the specific gravity falls below 1.220,

restored to their original chemical condition,

corrected to 80F., the battery should be

ready to deliver electricity again. Hydrogen and

recharged. The battery will be fully charged

oxygen gases are given off at the negative and

when all the cells are gassing or bubbling freely

positive plates respectively as the plates reach

and the specific gravity reading is 1.255 or

the fully charged condition. This is the result of

higher.

the decomposition of the water by an excess of

charging current not utilized by the plates.

If the batteries are allowed to remain in a

partially discharged state for a period of time,

3. Inspection

the lead sulphate which forms on the plates

during the normal chemical process of

The battery contains no electrolyte until it is

discharging hardens and reduces the capacity of

activated for service in the field. Consequently,

the battery. When the plates in a battery are in

it is referred to as a "dry-charge" battery.

this condition, the battery is referred to as

"sulphated."

Unless the batteries are kept dry until ready for

use, they may lose a portion of their activating

Fast charging a sulphate battery will only supply

capacity due to moisture oxidizing the pre-dried

a surface charge and will not reconvert all of the

plates.

hard lead sulphate to its original chemical state.

The hardened lead sulphate remaining on the

Dry charged batteries must be handled with care

plates will then continue its growth during normal

to protect them against breakage. This may not

operation, eventually resulting in a completely

be evident until the battery is activated by

discharged battery. Additional fast charging of a

adding electrolyte. Battery cartons should be

sulphated battery will damage the plates and

checked for evidence of either damp-

lead to premature battery failure.

R-146-1

3-72