FYI HOW-TO: Maintain your car battery & Terminals

[JC220]

This is a very overlooked service item IMO. This year alone I have helped people with 2no different cars that had sudden no start condition. In both cases the battery terminals had slight corrosion on them which made the car go dead momentarily.

This is TOTALLY avoidable. Your car needs a nice clean connection to the battery at all times. This thread is intended to give a little info on what I do to all of my cars to ensure I don’t have avoidable voltage issues or non start situations:

PART 1: The Battery.

You will need:

• Battery Terminal Grease
• Battery Terminal Cleaning Tool – like this:

• Fine scotch brite pads
• De-ionised Water
• Electrical Contact Cleaner
• Gloves & safety squints – you are dealing with acids here be careful…

Conventional batteries contain a liquid “electrolyte” which is a mixture of sulfuric acid and water. The plates in a lead battery contain an active material that should be continuously bathed in electrolytes while oxygen and hydrogen gas are released during charging.

While a battery should only be filled after it is completely charged, you should check the water level before charging. Before charging, make sure there is just enough water to cover any exposed plates. After charging, add enough water to bring the level to the bottom of the vent, about ¾ below the top of the cell.

It’s important to note that battery owners should never add sulfuric acid to their battery. During normal operation batteries will only consume water – and not sulfuric acid. When your battery’s electrolyte is observed to be low, filling the battery with water will keep the battery healthy and safe for use.



Step 1:

I like to periodically remove the battery from a car in my fleet at least every 6 months for a full recon / maintenance charge. Check the levels of electrolyte first just to ensure all plates are covered inside the battery at this point - and fully charge (Your favourite Noco or CTEK charger is ideal) This should extend the life of your battery long term. A fully charged battery will have a voltage of over 12.6 volts or above.



Step 2:

When fully charged start by checking and topping off the electrolyte levels in the cells. The level should be between the min & max markings on the battery body. On the S600 battery here I had one cell lower than the rest. It was at the min mark whereas all other cells were at Max. Therefore I decided to top off.

ONLY use De-ionised water available at Auto Parts Stores. You may have to cut plastic decals to expose the cell cap(s):



Carefully top off until all cells are even. Indicative photo showing the cell level indicators on this Varta Battery:



Step 3:

Use a battery terminal cleaning tool and take the worst of the tarnish off of both terminal posts:

Before:



Using Tool:



Step 4: Use the electrical contact cleaner and Fine scotch brite pads to carefully buff the terminals clean and shiny without removing any material. (Don’t use sandpaper as you will wear the lead posts away)



Step 5: I like to clean the battery down at this stage, Using a detail brush, APC and hot water with a microfiber towel to pat dry.



Step 6: Apply Battery Terminal Grease to fully coat both battery posts. Don’t go nuts this just has to exclude any air between the battery terminal in the car and the post to maintain and prevent corrosion from forming in the future.


At this stage you should have a JC220 approved Battery



However there is more to do in car.....

 

[JC220]

Part 2: Car inspection and Battery Installation good practice


Step 1: Inspection / Tray area. When was the last time you inspected underneath the battery tray in your 036? This is a fairly common potential rot point on the 500E and must be checked periodically to spot and address any issues early. Note the 124.036 battery area body sheet metal is NLA so you’re in trouble if it gets bad.

View with battery tray fully removed in my 500E: (I just re-painted this area inside to maintain it!)




Inspect the rubber drain plug(s) to be sure they are present and clear of debris. New Grommets are available as part number A1079972781:



If there are any signs of battery acid spill down here or in the battery tray itself you should neutralise and remove it with a solution of baking soda and water.


Step 2: Inspect and clean both battery terminals. Using the terminal tool brush attachment clean the inside contact areas of the terminals. Then use a suitable brass or similar brush with contact cleaner and clean the outer parts of the terminals:



I also cleaned the earth connection bushing on the car chassis rail:



Step 3: If all is good and rust free then proceed to re-install the Battery tray. Part number in the photos below of my recent new battery tray:



I chose to use Amber Cavity wax on the underside of the new battery tray and also in the fender well area. Doesn't look nice but this stuff sure works!! It forms a waxy / oily barrier against rust for many years.



Note the newly installed battery drain / vent pipe there. Very easy just drill the rear most rubber bung and push the hose through. It tucks neatly under the battery tray. However you MUST also bung the opposite side vent on the battery:



I purchased a sealed high CCA battery for my 500E. (AGM went to the V12 as its battery just died) Sealed batteries shouldn't leak anything during their lifetime but must still be vented for off gassing during charging and so that any possible acid drips or flammable gases are always safely discharged via the vent hose to outside of the car



Step 4: Re-install the battery tray:



Set the battery back in and ensure the battery clamp is re-installed:



Smear a little battery terminal grease inside the prepared terminal then connect the positive battery post first, followed by the negative. DO NOT overtighten clamp bolts. Tighten enough that you can no longer wiggle the terminal clamp by hand and you are good.



I also upgraded the m6 nut on the positive terminal to a Nyloc Nut. This connection is for the ECU coffin box feed up front so you want a nice clean & solid connection here.



I also installed a non original to the 500E MB positive terminal cover. This is until I sort my custom new 500E battery covers



Re-install the negative/ ground cable and I used a small smear of the terminal grease there too. Hook up the new battery vent hose and your done

 

[JC220]

Supplementary information to follow on correct Venting of your Battery.

To vent or not to vent? Short answer yes and that includes you “sealed” / AGM guys.

Whilst the 500E to my knowledge did not come with a battery vent pipe from factory – it is certainly a good idea to retrofit one at the earliest opportunity. (Assuming someone in the past hasn’t already done so)

MB did not start installing battery vent tubes as standard until later production years. Maybe 210s? And it is especially important when a battery is located inside the car trunk VS say in the engine compartment which benefits from free-flowing air.

What also compounds the need to install a vent tube IMO is the fact that many 500Es nowadays are not in daily service and are classic cars enjoyed at certain times of the year. This means that invariably the car battery will be hooked up to a battery charger / tender for prolonged periods of time which can be a higher risk of the battery off gassing explosive gases inside the trunk. (Hydrogen & Oxygen) Yes car batteries can explode during charging in certain circumstances.

BUT – I have a new-fangled Sealed AGM battery – I don’t need to vent it right??

Not so fast.

AGM batteries are a type of valve-regulated lead acid battery. They are “maintenance-free” in the sense of not requiring the addition of water to offset hydrogen gas released during the charging process. The glass mat in the battery absorbs the hydrogen produced prior to it escaping to the atmosphere allowing it to remain inside the battery.

But the “valve-regulated” part of the battery description refers to a vent. In the case of AGM, it’s a pressure-relief valve, usually opening between 1 and 2 psi. Charging too quickly produces hydrogen at a rate faster than it can be absorbed into the glass mat. If this occurs long enough, pressure will build inside the battery, and could force the valve to open. When this occurs, you’re suddenly releasing the accumulated hydrogen into the battery compartment. So you still need a location that’s free of ignition sources, and open to the atmosphere to dissipate the gas.

At about double the price, why buy AGM?

There are two key reasons to consider AGM batteries over flooded or “wet cell” lead acid batteries. First, there’s no water level to check or maintain. Second, by not having off-gassing under normal operation, you will see less corrosion in the battery compartment. That reduces maintenance of cables, and prolongs the life of other metal components in the battery bay.

In this How- To I will be showing how to add a vent pipe correctly to your battery

 

[JC220]

This is the reason for delay

When I bought my 500E some 4.5 years ago I went in here to maintain the battery sheetmetal. I decided at that time to retain the factory primer effect trunk and re-primed it all with a few minor repairs complete at that time. (A stitch in time saves 9!)

This time I went in and some tiny little brown flecks- whiffs really had appeared in a couple of areas where the spare tyre and carpets touched the primer.

So sod it- a rub down with fine scotch pads, pre paint wipe, another coat of etch primer and 3x coats of satin black. It needs a couple days to cure then I'll get the other posts complete.



The paint is still wet it will dry more uniform satin black then I'll clear Waxoyl too. Have the opposite trunk tub to spray too.

 

[gerryvz]

There are more than a couple of people on this forum whom I'm sure are heavily coveting that battery compartment sheet-metal. @Jlaa excepted, of course.

 

[JC220]

Yes the NLA 500E specific battery area sheetmetal is important to maintain. Which is a part of this thread when updated.

Here are some shots of people who were a tad too late to check this area out:





What you might typically expect to see if you get to it in time and count yourself lucky:



This is a very rot prone area. In part due to MB not fitting vent pipes to the batteries on 500Es from factory, possible acid leaks from the battery itself and or venting and the primer type finish in this area. Combine with people neglecting or just not knowing to check it out regularly and you have a potential headache brewing

 

[JC220]

Post number 3 is now complete. This is a common misconception that "sealed" AGM batteries do not require ventilation, but when you look into it, including battery manufacturers websites it is clearly recommended that proper vent provision is put in place. And dont forget to plug one end of the battery and vent the other end outside of the car.

I'll show how when part 2 is done in a couple days. Of course it's not rocket science either

 

[JC220]

Part 2 now completed! Comments/ observations welcome. Note I will have that battery hold down clamp re- yellow zinc plated soon

Although this area is preserved well in my 500E I will be removing that battery tray at least once a year to keep it that way.

Now - you guys can post pics of that you find down there!! Get inspecting before it's too late.

 

[JC220]

It's been a long day for me as I was going around the other battery Trays in the fleet too. Time for a:

 

[nocfn]

I vent my agm out the trunk vent with a long tube

 

[JC220]

I vent my agm out the trunk vent with a long tube

Do you mean the side rubber flap vents?

You could also use the front drain but I chose to leave it alone so all 3x drain holes in that bung stay functional.

Also - I tend to swap the batteries around in my cars every few months to spread the usage etc. So I vent them all the same side so I can drop in another battery and not have to swap the bung to the opposite battery vent.