Charging fault
Generator Battery Not Charging
A generator battery that keeps going flat usually has a charger, connection or battery fault, and we find out which before you buy a new battery. We test the mains battery charger, the battery itself, the terminals and fuses, the engine’s charge alternator and any drain on the battery, then give you a written quote.
Callout fee waived when you accept our written quote. 1-year workmanship guarantee. See prices
- We measure at the battery posts
- Charger, battery and wiring tested separately
- Written quote before any work
- Onsite across Gauteng
The battery will not recover
Why is my generator battery not charging?
Either the charge is not reaching the battery, or the battery can no longer hold it. Corrosion, a blown fuse or a failed charger stops the charge on the way. An old or worn-out battery refuses it when it arrives. We use a meter at the battery posts to tell which, because the light on the charger only shows that the charger has power.
If your set only starts after a jump-start, the charger is probably not keeping the battery topped up while the generator stands. It runs fine once started, then the battery is flat again at the next outage. That repeat pattern points to the charging side, not a one-off flat battery.
When the whole charging circuit needs work, such as a new charger, cables or an isolator, we handle it as a battery and charging system repair. Either way, you see the price in writing before we start.
Measured, not guessed
The battery readings we take
Resting voltage
A fully charged 12 V lead-acid battery reads about 12.65 V once it has rested for a few hours, according to Battery University. If a battery that has been on charge reads well below that, the charge is not getting through or the battery cannot hold it.
Charger float voltage
A charger holding a lead-acid battery at full charge typically floats it at 2.25 V to 2.30 V per cell, which is about 13.5 V to 13.8 V on a 12 V battery (Battery University). We measure it at the battery posts as well as at the charger, so a bad cable or terminal cannot hide.
Our technicians take these readings with the right instruments. You do not need to open the canopy or touch the battery before we arrive.
Fault guide
Generator battery not charging: what it can mean and what to do
A starter battery that goes flat or will not recover points to the battery itself, the mains battery charger or the engine’s charge alternator. We test each one separately. This guide separates what you can safely notice from what a qualified technician tests. One symptom never proves that a particular part has failed.
Symptom, likely cause and repair
Find the line closest to what you see. The cause is the most likely one, not a diagnosis: testing confirms it before any part is replaced.
| What you see | Likely cause | Usual repair |
|---|---|---|
| Battery flat after the set has stood | The battery charger is off, not wired or has failed | Battery and charging repairs |
| A charge alarm while the engine runs | A charging alternator or drive belt fault | Battery and charging repairs |
| Battery charges but will not hold it | A battery at the end of its life | Battery and charging repairs |
| Terminals corroded, or warm after cranking | Poor connections at the battery or the starter | Battery and charging repairs |
01
What you may notice
- The battery is flat when the generator is needed
- The generator only starts after a jump-start
- A charger fail or battery voltage alarm on the controller
- The battery is several years old or swollen
02
Possible causes
Any of these can produce the same symptom. Testing decides which one applies.
- A battery that no longer holds charge
- A failed mains battery charger or its supply
- A charge-alternator or regulator fault on the engine
- Loose or corroded terminals and connections
- A blown fuse in the charging circuit
- Parasitic drain from the controller or accessories
03
What you can safely check
Look and note only, from outside the canopy. Do not open panels, covers, fuel lines or the cooling system.
- What battery voltage does the controller show, if it displays one?
- Is there a charger fail or low battery alarm?
- How old is the battery, if it is labelled?
- Is the mains supply to the charger switched on?
04
Stop using the generator and call if you notice
- A swollen, leaking or hot battery
- A rotten-egg smell near the battery
- Sparking at the battery terminals
If it is safe to reach, stop the generator with its normal stop control or emergency stop, keep people away, and call a technician.
05
What a qualified technician typically tests
These are technician checks, not steps to try yourself. Several involve live electrical measurement, fuel or pressurised systems.
- Battery condition and load test
- Mains battery charger output and float voltage
- Engine charge alternator output while running
- Terminals, fuses and wiring in the charging circuit
06
Common repair categories
The repair follows the test result. These are the services this symptom most often leads to.
07
What to send when you book
- Your suburb and how we reach the generator
- Make, model and kVA from the data plate (a photo is ideal)
- Fuel type: diesel, petrol or gas
- The battery voltage or alarm shown on the controller
- The battery age, if known
08
Related faults and services
Not sure which symptom fits? Try the generator symptom finder.
Safety before you check anything
- Exhaust contains carbon monoxide, which you cannot see or smell. Run a portable generator outdoors only, away from doors, windows and vents, and never run any generator in a house, garage or other enclosed space.
- A standby generator set to automatic can start at any moment, when the mains fails or on its exercise timer. Keep the canopy closed and stay clear of fans, belts and the exhaust.
- Generator output, the changeover and the control panel can be live, and some parts hold stored electrical energy after shutdown. Leave panels, covers and wiring closed for us to open.
- The engine, exhaust and coolant stay hot after running. Never open a radiator or coolant cap on a hot engine.
- Do not refuel a running or hot generator. If you smell gas at a gas-fuelled set, do not operate switches; leave the area and contact your gas supplier.
Carbon monoxide guidance: US Consumer Product Safety Commission: Generators and engine-driven tools (carbon monoxide).
Send the details on WhatsApp
This opens WhatsApp with a short message already typed: brand, model, capacity, symptoms and suburb. Fill in what you know and send it. Blank lines are fine.
- The data-plate photo is added inside WhatsApp after the chat opens: tap the attachment or camera icon and choose the photo. A link cannot attach the photo for you.
- Take the photo only when the generator is switched off and has cooled down. Do not reach over or into a running or hot generator, and keep away from the exhaust.
- A standby generator set to automatic can start by itself when the mains supply fails. If you are not sure how it is set, photograph the plate from a distance or send a photo of the whole set instead.
Typical repair costs for this fault
Published ranges, last reviewed October 2026. The callout is R400 – R700 in business hours and R700 – R1,400 after hours, and it is waived if you accept the quote. Your written quote after diagnosis is the price that applies.
- Battery replacement
- R900 – R2,800
Step 9: book a diagnosis visit.
Related Pages
The charging system and other start faults
Common Questions
Questions about a generator battery that is not charging
Why is my generator battery not charging?
Usually because the charger has failed, a connection is corroded or loose, or the battery can no longer hold a charge. We measure the charger output and the battery voltage to tell which one it is.
It starts if I jump it, then dies next time. Is that the battery?
It could be, but it is also the classic sign of a charger that is not keeping the battery topped up while the set stands. We test both before you replace anything.
The charger light is on. Does that mean it is charging?
Not necessarily. The light shows that the charger has power. The voltage at the battery posts shows whether the charge is actually arriving.
Can corrosion stop a battery charging?
Yes. A green or white crust on a clamp can leave the charger working while the battery sits cut off from it. We clean and remake the joint, then measure again.
Could something else be draining the battery?
Yes. A small drain from the controller or an accessory can flatten a battery that charges normally. We check for a drain once we know the charger output is right.
Is this the same as a generator that will not start?
No. A no-start can be fuel, the starter or the controller. This fault is narrower: the battery is not being charged, so it goes flat between starts.
Should I keep jump-starting it?
No. A jump-start gets the engine turning once, but it does not fix the charger, cable or battery that will leave you flat at the next outage. Book a test instead. We are open 24/7 and arrive within 1 hour for breakdowns.
Still unsure what the fault is? Call or WhatsApp 082 057 4605 for onsite diagnosis.
Service Areas
Onsite visits across Gauteng
We come to your generator anywhere in Gauteng, 24/7. Choose your region for local suburbs, call-out details and the faults we see most there.
What to send before we attend
These details help us plan the visit and bring the right parts. Send what you can on WhatsApp; if you can’t find the model number, we still book the visit.
- Location
- The suburb or site, so the visit can be booked in the right area.
- Make and model
- The generator brand and model, if they are known.
- kVA
- The size printed on the data plate.
- Fuel type
- Diesel, petrol, LPG, natural gas, or dual-fuel.
- Controller model
- The module name on the panel, when it is visible.
- Fault or alarm
- What the set does, and any text on the screen.
- Photos
- The generator, the data plate, and the controller or alarm. Send these on WhatsApp.
Book a Visit
Tell us when the battery goes flat
Say whether it goes flat after standing, straight after a start, or with a charger alarm on the screen. Each one points us to a different first test.
- Call
- 082 057 4605
- Message us on WhatsApp
What happens next
- We reply with questions about the generator, or to book a visit.
- A technician comes to you. For a breakdown we arrive within 1 hour.
- The fault is diagnosed on site and you get a written quote. No work starts until you accept it.
Charlie, lead technician: Degree in Mechanical Engineering, Degree in Electrical Engineering, Diesel Plant Fitter. Generator specialists since 2000.