Battery or Alternator? How to Tell, and When to Call an Auto Electrician
It's seven in the morning, you turn the key and get a click. Or nothing at all. Most people's first thought is the battery, and often they're right. But a flat battery and a failing alternator can look almost identical from the driver's seat, and swapping the battery when the real problem is the charging system means you'll be stuck again within days.
Here's how to tell the two apart, what else can cause the same symptoms, and when it's time to bring the car to Transit's auto electricians on High Street in Wauchope.
The quick test most people can do
If the car jump starts and then runs fine all day, the battery is the usual suspect. It isn't holding its charge overnight.
If it jump starts, runs for a while and then dies again, or the headlights and dash dim while you're driving, think alternator. The alternator charges the battery while the engine is running. When it stops doing that, the car runs on whatever is left in the battery until there's nothing left.
Treat that as a rule of thumb rather than a diagnosis. Both parts can fail together, and a weak battery makes the alternator work harder.
Signs it's the battery
Slow, laboured cranking, usually worse on cold mornings
A clicking sound when you turn the key
The car has sat for a week or two and won't start
The battery is getting on. Most car batteries last somewhere around three to five years, and heat is hard on them
White or green corrosion building up on the terminals
Signs it's the alternator or charging system
The battery warning light comes on while you're driving. That light is about the charging system, not only the battery
Headlights or dash lights that dim or flicker, especially at idle
Electrics acting strangely: slow power windows, a radio that cuts out
A whining noise or a burning smell from the front of the engine, which can point to the alternator or its drive belt
A new battery that goes flat again quickly
When it's neither
Sometimes the battery is healthy, the alternator is charging, and something is quietly draining power with the engine off. Auto electricians call this a parasitic drain. Common culprits are accessories wired in without the right setup, like a dash cam on constant power, a fridge or lights in a 4WD, or a reverse camera fitted somewhere else. Loose or corroded earth connections cause similar headaches.
A drain has to be traced circuit by circuit. That's diagnostic work, and it's why guessing with new parts tends to get expensive.
Caravans, 4WDs and second batteries
If you run a fridge or lights off a second battery, the way it's wired matters as much as the battery itself. Many newer vehicles have smart alternators that vary their output, which is why dual battery systems on modern vehicles usually charge through a DC-DC charger. If your second battery never seems to fill up on the road, have it checked before your next trip.
Transit fits dual battery setups, caravan and trailer wiring and electric brake controllers, so the whole system can be looked at in one place.
How Transit tests it
Transit's auto electricians test the battery and the charging system before anything gets replaced. You're told what the fault is and what the fix costs before any work starts. If it is the battery, Century and Super Charge batteries are kept in stock, so most can be fitted the same visit.
“His knowledge was amazing and he was able to explain the problem in a way I could understand and also ensured I was safe to continue driving.”
Katie Moore, Google review
Common questions
Can I keep driving with the battery light on?
It's not one to ignore. If the alternator has stopped charging, the car is running on battery power alone and can cut out without much warning. Get it checked as soon as you can and avoid long drives until then.
How long does a car battery last?
Typically around three to five years. Hot weather, lots of short trips and extra accessories all shorten that.
Will a new battery fix a car that won't start?
Only if the battery is the problem. A new battery sitting on top of a charging fault will go flat too, which is why Transit tests both first.
Do you work on caravans and trailers?
Yes. Caravan, trailer and float wiring, electric brake controllers, solar connectors and inverters are all done in the workshop.
Book it in
Car won't start today? Calling is faster than the form. Transit's auto electricians are at 97 High Street, Wauchope, open Monday to Friday, 8am to 5pm. Call 02 5514 5018 or book a diagnosis online.
