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Electrical guides and mods

Battery Trickle Charger

If you don't use your smart that often, it's a good idea to keep the battery charged. Batteries can be managed and topped up using a trickle charger.

Modification Details

Trickle Chargers

A trickle charger maintains, charges and conditions the car's batteries whilst the car is not in use.
They plug directly into the mains power supply and charge the battery as and when it needs it.

They start with a standard charge until it's fully charged, then depending on the model, they will maintain the charge, condition the battery, equalise and desulphate (desulfate) the battery. In all, the battery is kept healthy.

The most well known chargers are made by Ctek and those are what I used on my cars.

Fitting A Trickle Charger

This is the 2nd Ctek charger I purchased, you can pick them up online from car sites and eBay.
You will want one that charges a 12 volt car battery.
(6 volt motorcycle chargers and 24 volt lorry chargers are available).

In the box you should get the charger, a bag, a manual and 2 sets of battery connections.

On the left is the permanent connections and on the right is the temporary connections.
They both terminate at a waterproof connector that the charger clips on to.

I don't see the point in the large clamp connections so we will be using the other type.

Fitting is easy. Undo the nut from the earthing stud that the battery is connected to. Put the black lug
on it and tighten the nut back up. The red lug connects directly to the battery positive terminal so undo
the nut, put the red lug in place and refit and retighten the nut.

Here is the pigtail lead connected to a Roadster...

...and here is a pigtale lead connected to the fortwo.

The leads are usually long enough to move the waterproof connector away from the
battery and somewhere more accessible making it easier to plug in when you need it. 

The waterproof connector can be discretely hidden away.

The charger can then be attached and plugged into the mains to begin the charging.

Ctek also sell a flush mounted indicator panel which can neaten the installation.

The panel has 3 lights that inform you of the battery state.

Fitting is very easy. Find a suitable plastic trim with room behind it for the panel to fit.

Cut out a hole the correct size.

Push the wires through the hole and seat the indicator panel in position.

As before, the charger can now plug directly into the waterproof connector.


The pigtail connections are waterproof and so is the entire indicator panel so there is no issue running the
lead from the battery into an exposed area. You can even install the indicator panel on the outside of the car.

The instructions state that the actual charger units are also waterproof but I haven't tested them.
Just remember that the mains plug is not waterproof so this part should always be indoors or in a specially designed
exterior mains socket with a waterproof lid/seal. If you use an extension lead, none of that is waterproof.

Types Of Ctek Charger

I only have 2 but their range updates regularly and the specs change so go with whatever you require.

My first Ctek charger was a basic XS800 which charges the battery and cuts off when it's fully charged. It then
allows the battery level to drop slightly over time before it begins to charge it again. This stops over charging.

The next Ctek charger I bought has more functions. It has 5 more LEDs, it must be better.
This charger will charge, condition, read it a bedtime story and tuck it in at night.

LED 1 - Desulphation
LED 2 - Bulk
LED 3 - Absorbtion
LED 4 - Analyse
LED 5 - Float
LED 6 - Pulse

Neither of these chargers cost me more than a new battery so it's cheaper to look after the battery
you have instead of replacing it because the battery went flat and it was never the same again.

Desulphation, Bulk, Absorption...What?

If you have a Ctek charger with several charging programs like my XS 0.8 then this is what they do.


Lead and lead dioxide are the 2 active materials on a battery's plates, these react with the sulphuric acid to form
lead sulphate. When the battery is being charged (engine running or on a battery charger), the lead sulphate is
broken back down into lead and lead dioxide. However, if the battery is not charged and left to go flat, the lead
sulphate crystalises on the lead plates and these crystals do not dissolve when the battery is charged.

The lead plates have to be in contact with the sulphuric acid to create a charge. If the lead plates are covered
in crystalised lead sulphate then these crystals create a barrier between the plates and the sulphuric acid.

This reduces the amount of power that the battery can produce. Eventually it won't start the car.
Highly sulphated batteries will still show a 12v output but won't create a high enough amperage.
Sulphation also increases charging times and cause higher battery temperatures.

A desulphation program on a charger detects the sulphation and attempts to remove the build up of crystals
on the plate by pulsing the voltage and current. The effectiveness depends on the state of battery.

Soft Start (not on mine)

Uses a lower voltage (12.6 volts) for an initial charge to ensure the battery will accept a charge.


After the desulphation process is complete, the charger will charge the battery with maximum
current until it is at approximately 80% of its capacity. This is the main charging phase.


Picking up from the previous charging program it continues to charge with a declining current to bring
the battery up to a 100% charge capacity. The declining current means the battery is never over charged.


Now the charging is complete, the charger checks the output of the battery to ensure it can hold a charge.
The battery should maintain a voltage over 12 volts when resting. This only takes a few minutes.

Recondition (not on mine)

This is a separately selectable mid program on some higher end Ctek chargers.
Higher voltage (15.8 volts) and a lower amperage is used to create controlled gassing.
Gassing helps to mix the acid and water to increase power and efficiency at the lead plates.


The bulk and absorption programs charged the battery with 14.4 volts. The float
program charges at 13.6 volts to maintain the battery voltage at maximum level.


This final program maintains the battery's capacity at 95 - 100%. The charger monitors
the battery voltage and gives a pulse when necessary to keep the battery fully charged.

Which Program Do I Choose?

That's the great thing about Ctek chargers, they are clever enough to know themslves.
You just plug it into the battery and let the charger do what it thinks is best.

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