Battery - Discharge Precaution During Very Low Useage
84mercedes02TO: OUR MERCEDES-BENZ PASSENGER CAR---DEALERS
DATE: May, 1984 REF. NO. MBNA 54/8
SUBJECT: BATTERY CARE FOR VEHICLES IN DEALER STOCK AND SHOWROOM DISPLAY
To reduce the discharge rate of batteries in stock vehicles, the negative terminal should be disconnected. This will eliminate the discharge of the battery caused by electrical components which constantly draw a small amount of current, even though they are switched off (e.g.. electronic radio, alarm system, etc.).
There is always some chemical activity in a battery even when the battery is not connected to a circuit or delivering current. Such chemical action, which does not produce current, is termed "self-discharge".
The lead sulfate produced by self-discharge is harder to break down during recharging of the battery. If batteries are not recharged periodically to compensate for selfdischarge, they may be severly damaged or even completely ruined.
The following maintenance procedures will help prevent battery discharge problems:
FIGURE 1 - REFILLING BATTERY:
1. It must become common practice to fully charge the battery before a vehicle is delivered to the customer.
2. During every service, refill the battery with distilled or tap water. The battery is completely filled when the water stops draining through the overfillprotection diaphragm (Figure 1).
3. Check the fluid level in each cell approximately every 4 weeks; more frequently during the summer and in hot climates, by refilling them as outlined in step 2.
4. Periodically coat the battery terminal clamps with acid-proof grease. Keep the battery clean and dry.
NOTE: Always remember to follow the battery charger manufacturer's operating instructions and to wear eye protection when connecting or disconnecting the battery charger.
Vehicles in stock, demonstrators, and showroom display are especially susceptible to self-discharge and should therefore be handled as follows:
Vehicles in Stock and Demonstrators
These vehicles are seldom driven or in most cases not at all. Inspection of the batteries of such vehicles indicates that they are being gradually discharged. These batteries must be charged on a regular basis, otherwise they will become partially or totally sulfated.
Our recommendation is that the battery electrolyte level and concentration are checked at least once a month. The table below gives the battery charge condition with the specific gravity of the electrolyte at 20~C (68~F).
Battery charge Electrolyte
Recommendation
condition specific gravity
Fully charged 1.28 none
Half charged 1.20 recharging necessary
Discharged 1.12 recharge immediately
When charging the battery, keep in mind the following:
- The specific gravity of the electrolyte decreases with increasing temperature by 0.01 for every 15~C (27~F) difference in temperature.
- Disconnect the negative battery terminal if the battery is left in the vehicle.
- The charging current should be 10% of the battery capacity (for example, approx. 9A for an 88A-h battery).
FIGURE 2 - CHECKING ELECTROLYTE SPECIFIC GRAVITY WITH HYDROMETER:
FIGURE 3 - REFRACTOMETER:
- After charging, check the specific gravity with a hydrometer (Figure 2) or a refractometer (Figure 3) and, if necessary, add distilled or tap water to bring the electrolyte up to the proper level.
Vehicles in Showroom Display
These vehicles are subjected to continuous battery discharge - due to demonstrations of electrical accessories which drain the battery. Experience has shown that due to the prolonged discharge state, these batteries may have to be scrapped because of severe sulfation.
Therefore, batteries of vehicles in showroom display have to be removed every three weeks and recharged completely.
We are presently testing a low current battery charger that is small enough to be concealed under the hood. Using such a battery tester would eliminate removal of the battery for recharging. We will inform you about its approval as soon as possible.
Your cooperation in following all of these guidelines will greatly increase the service life of these batteries. Warranty claims for batteries showing signs of faulty maintenance will not be accepted in the future.
For additional information on batteries with overfill protection, refer to S.I. 54/17, December 1978 (included in Service Microfiche, Service Information Passenger Cars, 1972 through 1979, Group 54).