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Pelican Technical Article:

Battery Replacement

Ken Freund

Time:

15 minutes15 mins

Tab:

$150 to $275

Talent:

*

Tools:

13mm wrench, battery terminal puller (optional), post & terminal cleaner, 10mm socket, extension and ratchet on early models for hold-down bracket

Applicable Models:

Mercedes-Benz 450SL (1973-80)

Parts Required:

Battery

Hot Tip:

If battery is under hood, allow engine to cool

Performance Gain:

Reliable starting

Complementary Modification:

Test battery and charging system, replace cables, replace alternator belt

Early R107 models (350SL & 450SL in USA) have the battery located on the right (passenger side in US) of the engine compartment. With the introduction of catalytic converters, battery location was moved to the right side of the trunk compartment. The early models have a smaller battery, which is held in place by a bracket at its base on the side facing the engine. Later models have a larger battery that is inside a black plastic case, hidden behind a hinged upholstered panel on the right side of the trunk. Power from the later-model batteries is routed forward via the positive cable to a large terminal block mounted on the right inner fender and frame extension, just forward of the firewall.

Before replacement, batteries and charging systems should be tested. Loose or dirty terminals or connections, a slipping belt, faulty voltage regulator or alternator can cause a battery to become discharged. Sometimes batteries go dead while the vehicle is parked because of current drains, such as alarms, trunk lights or glove box lights that stay on, etc. With the engine and all accessories turned off, check for current flow between the battery and vehicle. Current should not exceed about 0.050 amperes (50 milliamps). With the engine running at a fast idle, voltage measured across the battery terminals should be about 13.6 to 14.4 volts. A fully charged battery at rest (no load or charging) should measure about 12.6 volts. A battery maintenance charger (not a regular trickle charger) should be used if the vehicle is stored for more than a week at a time.

Warnings

Always use caution when handling batteries. Batteries vent explosive hydrogen gas and contain toxic lead and extremely corrosive sulfuric acid, which can cause severe burns and blindness. Wear eye protection and rubber gloves when handling batteries and avoid contact with skin or clothing, as acid may injure skin and eat holes in cloth. Baking soda and water can help neutralize spilled acid. Avoid making sparks when connecting battery chargers, by plugging them in after making connections. Avoid making sparks near the battery when connecting jumper cables, by making the last (ground or negative terminal) connection to a clean chassis ground.

Remove & Install

On early models with under hood batteries, remove the two 6mm nuts (10mm wrench size) located at the base of the battery on the engine side.

On later models, open the trunk and locate the battery access cover on the right side. Turn the black plastic knob and open the hinged access panel. Unclasp the two metal buckles which secure the plastic lid on the battery case and lift the lid away.

On all batteries, loosen the battery cable clamps. Start with the negative terminal, because if the wrench contacts any grounded metal it won't spark or superheat the tool.

Disconnect the negative battery cable terminal. If it is difficult to remove, remove the through bolt and twist a large screwdriver in the gap to slightly spread the two sides. Or, if you have a terminal puller tool, use it now.

Remove the positive cable terminal in the same manner.

Lift the battery out of the vehicle. On batteries with removable caps, check electrolyte level and top up as needed with distilled water.

Clean and inspect the terminals, using a special terminal-cleaning tool. Buildup of corrosive powder can be neutralized and removed with a mixture of baking soda and water and a rag (wear eye protection and rubber gloves).

Reinstall the battery, and hold-down bracket if equipped.

Reconnect the cable terminals, positive first, then negative.

On trunk-mounted batteries, reinstall the cover and secure it, then close the access panel.

On earlier models, the battery is located under the hood on the right side near the firewall.
Figure 1

On earlier models, the battery is located under the hood on the right side near the firewall.

On later models, the battery is located behind an upholstered panel in the trunk.
Figure 2

On later models, the battery is located behind an upholstered panel in the trunk.

Twist the knob 1/4 turn and pull the panel toward you.
Figure 3

Twist the knob 1/4 turn and pull the panel toward you.

The battery box lid is held in place by two metal straps with buckles.
Figure 4

The battery box lid is held in place by two metal straps with buckles.

Pull on the buckles to open them and then separate the straps so the lid can be removed.
Figure 5

Pull on the buckles to open them and then separate the straps so the lid can be removed.

Slip the lid out of the compartment.
Figure 6

Slip the lid out of the compartment. CAUTION: Make sure the metal straps do not contact the positive battery terminal (front) as you remove the lid.

Disconnect the negative battery terminal first (reconnect it last).
Figure 7

Disconnect the negative battery terminal first (reconnect it last).

Disconnect the positive battery terminal next (reconnect it first).
Figure 8

Disconnect the positive battery terminal next (reconnect it first).

If terminals are stuck, use a terminal puller such as this.
Figure 9

If terminals are stuck, use a terminal puller such as this.

If the battery posts are corroded, clean them with a terminal-cleaning tool.
Figure 10

If the battery posts are corroded, clean them with a terminal-cleaning tool.

If the battery cable terminals are corroded, clean them with a terminal-cleaning tool.
Figure 11

If the battery cable terminals are corroded, clean them with a terminal-cleaning tool.

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Comments and Suggestions:
Debbie Comments: I have a '79 450 sl with a dead batter and can't open the trunk. I have tried over and over locking and unlocking the driver door to try and get trunk lock to release but it won't. I can't get the trunk open when using the key on it either - no matter how I turn the key.
November 25, 2016
  Followup from the Pelican Staff: Press down on the trunk lid while trying to use key. Something may be jammed in the latch. I have seen that before. Press down, unlock, pull up. - Nick at Pelican Parts  
Bob Comments: If the battery is dead on a '79 how do you get the trunk open?
October 30, 2016
  Followup from the Pelican Staff: key in the lock cylinder won't do it? - Nick at Pelican Parts  
Bindi Comments: Can anyone tell me where the Battery vent is on a 1988 560sl. My new battery has a vent but I can't find anything relating to a vent tube, either physically or thru manuals. Should I be using a non venting battery.
June 27, 2016
  Followup from the Pelican Staff: There should be a vent that runs out the trunk. Remove the battery and check around the battery tray area. - Nick at Pelican Parts  
Dan Comments: I have a 1987 560SL and had some one jump the battery which started the car but after driving the car for some time parked the car and it would not start but the lights went on but there were no sounds or turning over. I have not touched the car since.
March 8, 2016
  Followup from the Pelican Staff: The battery may be faulty or you crossed the cables and blew fuses during the jump start. Check battery voltage and voltage at the main fuse panel. - Nick at Pelican Parts  
Don Comments: My '73 MB 450SL must also need the "small" battery, as Group 49 battery the books call for is 2" too long for the tray. What group size/type battery fits this car?
January 3, 2016
  Followup from the Pelican Staff: Everything I see says group 93 or 49. To be sure, Give our parts specialists a call at 1-310-626-8765
- Nick at Pelican Parts
 
Bill Comments: How about some factory battery dimensions for the early "small" battery in '73 450SL? thanks
April 20, 2014
  Followup from the Pelican Staff: I couldn't find your specific model, but a similar one:
Termination: TOP POST (AUTO TYPE)
Length: 10.91"
Height: 7.47" - Nick at Pelican Parts
 

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Page last updated: Fri 12/9/2016 02:30:42 AM