Hooking a trickle charger to a car battery can be a reliable way to keep the car battery charge topped up if you plan to park your car for several days or longer.
Much as connecting the charger to the battery should be straightforward, it can fail to charge it.
This post explains why a trickle charger can fail to charge a car battery and what you can do to get it working.
Why a Trickle Charger May Not Be Charging the Battery? What to Do
If there’s no noticeable change in the battery voltage or no current flowing into the battery, it might be:
1. The trickle charge positive and negative cables are reversed or damaged. Confirm that the positive lead from the trickle charger connects to the positive battery terminal and the negative lead to the negative battery posts.
Check that the charger clamps are making firm contact with the battery posts. Remove any corrosion that may have formed and is restricting the flow of current to the battery.
2. If using a 120V trickle charger, confirm if the charger is plugged into the wall outlet. Is the wall outlet switched on? This too can stop a charger from working.
3. You may need to allow for more time for the trickle charger to make a noticeable change in battery voltage. Some trickle chargers are only able to supply up to 1 amp of current.
If the battery is severely depleted, considering a 50 Ah battery, you may need at least 2-3 days to get it charged again.
Use an external charger with a higher charging current to speed up the charging process.
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3. The battery may be dead. A dead battery will not be able to accept or hold charge. You can have the car battery tested at a reputable car repair shop.
If confirmed as damaged, replace it. If it is still under warranty, you can get a replacement.
4. The trickle charger may be faulty. Does the trickle charger have any LED display indicators confirming the charging status of the battery?
If it does and they are blank or instead display an error status, it is possible that the charger is faulty.
Contact the charger manufacturer for support or a replacement.
What Shows a Trickle Charger is not Charging?
The surest way to tell if a trickle charger is charging the battery is to either monitor the battery voltage or the current flowing into the battery using a clamp-on meter set to read DC amps.
Some models of trickle chargers have inbuilt LEDs to display the battery charge status. You can use this to check if indeed the trickle charger is working.
Note: Since the trickle charger is a slow charger, it may be a while before you notice a large enough change in battery voltage. Be ready to wait for a while!
For example, at a charge rate of 1 amp, after 5 hours, the battery capacity change will be about 5 Ah which works out to be only 10% of the capacity of a 50Ah battery.
How Long a Trickle Charger Takes to Charge a Battery
There’re several variables at play. Charging time mainly depends on the battery capacity and how deeply discharged the battery is.
Note: In cases where the battery is damaged, it may not be able to charge the battery.
The table below shows indicative charge times for selected batteries using a 1 amp charger. This assumes that the battery has only been discharged to 50% of its capacity.
| No | Battery Capacity (Ah) | Charge time (hours) |
| 1 | 8 | 6 |
| 2 | 12 | 9 |
| 3 | 18 | 12 |
| 4 | 24 | 18 |
| 5 | 30 | 22.5 |
Related Questions
Will a Trickle Charger Charge a Dead Battery?
There is no guarantee that a trickle charger (1 amp or lower) will be able to revive a dead battery. In some cases, particularly if the battery voltage is as low as 1 volt or less, trickle charging may be able to raise the voltage high enough for a 2, 5, or 10-amp battery charger to charge it fully.
Trickle chargers in general are designed to maintain the charge of fully charged batteries and can take too long to charge.
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Closing Thoughts
Trickle chargers are slow chargers. They are designed to maintain the charge of already charged batteries and so, it may be a while before the battery charge status changes.
If your trickle charger does not seem to be working, check that its cables are not reversed or damaged, that it’s plugged into a wall outlet, and that it’s switched On. it is also possible that the battery may be dead and cannot be charged or that the trickle charger is faulty.
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