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Many modern cars are now fitted with Idle-Stop-Start (ISS), a technology which saves fuel & CO2 by stopping the engine when the vehicle is halted in traffic.

This technology needs a special car battery as the frequent restarts quickly damage a normal car battery and can invalidate the vehicle and battery warranty. If in any doubt please call us before selecting or fitting a Stop-Start replacement battery. You can read more about Stop Start systems below.

ISS Fitting

We have a lot of experience in fitting the correct type of battery for cars fitted with Idle Stop Start systems. The first thing is to identify the type of battery and replace it "Like for Like". We only replace EFB (= Wet/Flooded), or AGM (VRLA = Dry Sealed) only with the same type of battery.

Having replaced the battery with the right type, we then use the On-Board Computer (OBC) port to ensure that the vehicle computer is reprogrammed - so that it "knows" it has a new battery and adjusts its charging accordingly.

Idle Stop Start System -  Overview.

Vehicles fitted with Stop Start systems often have upgraded components, for example Dual-Solenoid Starting Motors, Computer-controlled Variable-Voltage Alternators, upgraded lubrication & bearings, and sometimes an integrated high voltage Starter-Generator (to replace a separate starter motor and alternator).

The key point to note is that the Battery is a major component in the system and also needs to be upgraded from the conventional battery fitted to other models. If you fit a conventional battery, or the wrong type of upgraded battery, you may damage the system and invalidate the warranty of both the battery and the vehicle.

Conventional or "Basic" Stop Start Systems (EFB Batteries).

ISS systems (sometimes called "Stop and Go", i-Stop or Micro Hybrid) come in a range of different complexities.

The basic systems tend to simply use the battery to re-start the engine once the traffic starts moving. They sense the engine temperature, cabin temperature and the electrical load on the system and if any of these are outside certain limits (e.g. the aircon is running on a hot day, or the engine is cold) then the system won't stop the engine even at standstill.

Basic ISS systems often use the EFB (wet/Flooded) type battery, which is similar to conventional start batteries in construction except upgraded to deal with the demand for multiple starts in a journey, and hence designed to cope with a "deeper cycle" than a normal battery.

A deep cycle is where the battery loses power to starting multiple times, and hence cycles deeply into its reserve capacity as it is not constantly being replenished by the alternator as it would be on a car without ISS.

This requirement to deal with starting the car when only having "partial charge" is a major design challenge. The EFB design has porous fibre materials and thicker plates. Special low pressure contact materials on the battery plates allows better retention of the active material and guards against plate growth. The plate design is also enhanced, giving up to twice the normal cycling endurance versus a conventional car battery and up to 15% more cranking power.

Advanced Stop Start Systems (AGM Batteries).

More advanced ISS Systems often incorporate Regenerative Braking (capturing power by turning the kinetic braking energy into electrical power stored in the battery or a capacitor). They can often demand more power from the battery to run electrical loads or to provide an active power boost for the vehicle.

European models with Advanced ISS often use the dry AGM/VRLA technology.

These advanced systems need to quickly re-charge the battery in bursts, needing very high rates of charge acceptance (ie. very low internal resistance). AGM batteries use a fibreglass mat to absorb the electrolyte (acid) and hold it in high compression against the plates, providing very low resistance and the ability to cycle at least three times better than conventional batteries.

As AGM batteries are "dry sealed", they can be placed inside the boot or the cabin and will not gas-off under normal conditions. They incorporate a low pressure valve which vents to protect the battery from rupture in the case of fault or over-charging. For this reason they are sometimes also called VRLA (Valve Regulated Lead Acid).

AGM Batteries feature: 

  • Higher cranking power even at low states of charge
  • Improved cycling ability and rapid charge acceptance
  • Higher reserve capacity to power accessories during "engine off" periods

We stock the Varta range of AGM batteries - made in Germany and often the original factory fit for European models. We also have access to other brands where cost is an issue - call us for details.

How effective are ISS Systems in practice?

Its hard to say. Manufacturers claim fuel savings of 3-5% or so for Basic Start Stop Systems, and up to 8% for more advanced systems (with associated reductions in CO2).

Most motoring writers report some fuel savings but not that much, and often in real world conditions it is hard to get perfect back-to-back testing conditions. It is also heavily dependent on driving style. Also early ISS models in Australia were often diesel manual transmissions, which are not the most popular.

Mazda rolled out ISS in good numbers from 2010 but we heard in the early years of battery failures which required dealer visits to upgrade the charging algorithm or turn off the feature as well as replace the battery.

The systems will of course be getting better all the time, and Mazda's current i-Stop system (part of the Skyactive suite of fuel saving design features) features crankshaft sensing technology to use combustion to restart the engine.

Their E-Loop system adds regenerative braking and power distribution via a  Super-capacitor. Some Canadian reports do show good fuel savings for Skyactiv equipped models versus their previous cars, but again its hard to say how much of that is down to the Idle Start Stop system.