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Car Battery Maintenance

Mod Description
Battery maintenance is a dying art with the newest generation of car owners so lets bring it back to the people
Mod Details
PremiumNo Difficulty Mod ID731 Creditevilution Cost££1+ For450 Fortwo451 Fortwo452 Roadster453 Fortwo/Forfour454 Forfour Link Copy to Clipboard

The battery fitted to my Roadster is very similar to all the other Banner batteries fitted to smarts at the factory. It’s not a great battery, in fact the label only has 2 stars on it which usually means it is guaranteed for 3 years. After that, it’ll start becoming less efficient at starting your car, moving the clutch, selecting gears, running the engine and powering your headlights.However, good battery maintenance can increase the life and efficiency of your battery by many times. In the “good old days”, battery maintenance was practiced by most people and many old and classic cars are still on their original battery.

Batteries haven’t changed much but attitudes have. The throw-away culture we live in plus the need for companies to sell you a new battery every 3 years has lead to us leaving the battery alone and changing it for new when it dies.

Car batteries contain lead and an acid solution. Both of which is bad for the planet. So surely it makes more sense to look after what you have, save yourself money and not fill your municipal dump with acid filled boxes.

Battery Construction

Batteries are very basic. They have lead plates and acid all housed in a plastic box. The acid solution is 35% Sulphuric Acid and 65% water.

Gassing And Venting

When a lead acid battery is charged it turns some of the water back to Hydrogen and Oxygen. Hydrogen is flammable and the oxygen will make it burn more vigorously. The battery in the smart fortwo has a pipe leading from the battery to the outside of the car. If it didn’t, the cabin could fill with an explosive gas which wouldn’t be good.

Flat Battery

If you run a battery flat, a process called sulfation occurs. This is where the lead and acid react to create lead sulfate. The lead sulfate turns into crystals on the lead plates which reduces the amount of surface area in contact with the acid. The less surface area you have, the less power the battery can create. A battery that has been flattened will only hold about 50% of the amperage yet the voltage will remain the same and it will seem to charge OK.

Some battery chargers have a desulfation setting that attempts to break down the crystals on the plates. This is only really effective on newly flattened batteries and even after desulfation, it will never hold the same charge. The best thing to do is to get a new one and look after it.

How Flat Is Flat?

A lead acid battery only has to lose 20% of its capacity to be regarded as deeply discharged.

Regular Maintenance

If you have a trickle charger or standard charger with a desulfation parameter, connecting it monthly will keep the lead plates clear of corrosion. The most common trickle charger brand, Ctek, doesn’t do a great job at desulfation according to test results by If you are on the hunt for a good charger, look for a PulseTech or BatteryMinder brand charger. They aren’t the cheapest charger but if it adds a prejected 10 years onto the life of your battery, it’ll pay for itself in less than 4 years when you’d normally have to buy a replacement stop/start AGM battery or 8 years if you buy good quality SLA battery.

Checking The Electrolyte And Topping Up

When the battery is charged, some of the water is converted to gas and vented. So, over time, the fluid level goes down. Luckily enough it is only the water that is used and not the acid so you can top up the fluid to maintain the battery. Remove the battery from the car following this guide.

This is a standard smart battery. On the top are lids to the separate cells, these unscrew.

<p>As I have previously said, batteries contain acid and it won’t do you any favours if you get it on your skin or in your eyes so be careful and any safety wear like goggles or gloves would be a bonus.</p>
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Once you have unscrewed the lids, look inside and you should see a maximum level indicator. Chances are, your fluid levels will be low as mine were. Time to top them up.

Your cheapest option is to go to a car place like Halfords and buy distilled water, de-ionised water or “battery top up water”. Even from an expensive company like Halfords, 1 litre of this will only cost about £1. This is 39 times cheaper than a new battery.

Alternatively, if you have accidentally spilled fluid from the battery you can buy premixed acid solution to top it up.
This is not necessary if you are just topping up.

Top each cell up until you get to the maximum indicator mark and nearly/just cover it.

If you are going for a long drive (more than 1 hour) then that’s fine, if not, get the battery on charge. A proper charge is better than a quick cycle charge. I bought this charger from Argos and I only bought it because it was orange.

When the battery is charged fully, remove it from the charger and refit it to the car. It’s worth checking the battery levels every 6 months. Check your battery charger instructions to make sure that when the battery is charged, charging is stopped. Over charging a battery can damage it just as much as flattening it.

What Do I Do With My Old Dead Battery?

It goes without saying that you should take it to the dump so it will be dealt with properly. Even though the acid solution is almost exactly the same make up and ratio as patio cleaner, I can’t recommend that you use the contents for that purpose.