Flat batteries and jump-starting vehicles with flat batteries

Peter Jones • August 26, 2020

This is a bit of a long-winded explanation, apologies for that but there isn’t a brief way of describing it. If you don’t want to damage the electrical system in your car and have to spend a lot of money repairing it, please do read on:


I was listening to a conversation on our radio station the other day about batteries and jump-starting vehicles and this raised some concerns with me.


Some vehicles now have the battery tucked away under seats, floors or in the boot, so the manufacturers put a positive terminal and earth stud under the bonnet that can be used to jump-start the vehicle. We also use it to charge the battery and attach a battery support device when servicing and repairing the vehicle.


Jump-starting modern vehicles should be undertaken with great care as these vehicles have multiple electronic devices that can be damaged with voltage spikes. These spikes can occur once you have jump-started a vehicle and removed the jump cables.


The charging system and battery in a modern vehicle works very differently from yesteryears. The battery construction is different from our old lead acid batteries. We now have Calcium, AGM (Active Glass Mat), Gel and Enhanced Flooded batteries. All require a different charging process. 


The alternator (the device that charges the battery in the vehicle) is usually now controlled by a computer and works differently from our older vehicles. The alternator is there to maintain the battery at the correct voltage but CANNOT recharge a battery if it has gone flat. It will only put a surface charge on the battery. If the battery is not charged correctly it could have an adverse effect on the alternator as the alternator will be working overtime to try and charge the battery.


You may also have other devices on the vehicle that stop working because of the battery not being fully charged. This is called “power shedding”.


If you have had a flat battery you must get it charged and tested. Driving the car around for 20 minutes to an hour will not charge your battery properly. Because of the different battery construction, you would need to use a Smart battery charger – these chargers take the battery through different processes to charge them properly. Unfortunately the old battery charger that you have had sitting in the shed for the past few years is no longer up to the task.


In summary, only jump start your vehicle if you really know what you are doing. If your battery has gone flat it needs to be charged on a Smart charger. If replacing your battery, the correct battery must be fitted to your vehicle and in some cases the new battery will need to be coded to the vehicle so the charging system can keep in charged correctly.


If this hasn’t covered everything please ring one of the team at Petermark and we will be more than happy to answer your questions.


Peter Jones

Old dogs go WOF!

By Anne Jones • November 17, 2022
Petermark Automotive add WOFs to their list of services
The importance of regular servicing

The importance of regular servicing

By Peter Jones • June 4, 2021
The video and photos attached show the importance of regular servicing and oil changes, this is an extreme example. I know we sound like stuck records going on about why long-interval servicing doesn't work, but if you were faced with a $7000.00 repair bill and a long time off the road I think you would understand why we push this issue. Unfortunately even after the vehicle has been repaired we believe the engine will not last as long as it should do if it had been looked after. This vehicle has not had regular servicing. The turbo charger failed and on inspection we discovered that the oil had turned to an almost solid-like jelly, blocking the oil galleries which has led to the failure. We highly recommend having your vehicle serviced at a minimum of 10,000kms or 12 months whichever comes first.

The aftermath of Covid on our business

By Anne Jones • October 22, 2020
Are you like us in that certain words or phrases that have appeared since the beginning of the year make your blood run cold? Words like “unprecedented times”, “clusters”, “tricky virus” or “the new normal” – ugh! We have been very fortunate in our industry in that we have so far survived the Covid Pandemic thanks mainly to the Government for assistance packages and also for the loyalty of our clients who continue to support our workshop. We have been able to continue to operate our business as we did before and are forever grateful that the only time we had to close down completely was over those five weeks during Lockdown 4. We have however noticed a few minor problems that have an impact on the speed and proficiency of servicing or repairing our client’s vehicles. In the past we prided ourselves on a reasonable turnaround. Unless it was a major repair, we could almost guarantee that a vehicle would be in and out in a day. In some cases now though, we are having to wait for over a day, sometimes two for parts to arrive from a warehouse that might be just over the other side of the Harbour Bridge and not to mention how long it is taking for parts to arrive from overseas! It is disappointing for us that we are having to wait so long for parts to arrive but we understand how disappointing it must be for our clients too and we thank you heaps for your patience and understanding. This is causing a “cluster” f*** and “tricky” to work around - but is this the “new normal” during these “unprecedented times”? 😜 🚘 😷 🧴 👏
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