Selecting a charge rate for your drained car’s battery involves finding a charge rate to quickly recharge your battery that has no long-lasting damage to the lifespan of the battery. Charging at 15 amps is a good middle position, not too slow, and probably not too high to affect your battery lifespan depending on the battery size.
In this post, I cover:
- how long it takes to charge a 12V battery at 15 amps,
- whether it is safe to use
- which battery sizes (Ah) it is suited to
- which features to look for in a 15 amp charger
How Long to Charge a 12V Car Battery at 15 Amps?
Partially Discharged Battery (50%)
A 15 amp battery charger takes about 2 hours to fully charge a 12V, 50 Ah car battery, assuming it has been discharged to 50% of its capacity. The actual time to fully charge depends on several factors – battery capacity, depth of discharge, and temperature.
If the battery is more deeply discharged or dead, the charge time will be considerably longer than the 2-hour estimate for a 12V, 50Ah battery.
Battery capacity (Ah) and Charge Time (hours)
Larger capacity batteries will take a longer time to fully charge. For example, a 100Ah battery will probably charge in about 4-5 hours.
Note: These are estimated charging times that assume that the battery is only 50% discharged.
So, temperature, depth of discharge, and battery capacity combined contribute to the actual time it takes to charge a car battery with a 50 amp charger.
Is It Safe to Use a 15 amp Battery Charger?
Yes, it is generally safe to use a good quality 15 amp battery charger with at least a 40Ah battery or larger. Confirm that it has the auto-shutoff feature to stop or reduce the charging current when the battery is fully charged if you plan to leave it connected for a long time.
Connecting smaller battery sizes less than 40Ah risks damage to them from the higher than recommended bulk and float charge currents that can cause damage to the battery unless the charger has a lower current mode for smaller capacity batteries.
To minimize the risk of explosion, fire, or injury,
- charge the battery in a well-ventilated area.
- Only connect battery types that your charger supports. If the charger only charges AGM batteries, do not connect a Lithium ion phosphate battery for instance.
- Do not charge damaged or frozen batteries
When to Use a 15 amp Battery Charger?
A 15 amp battery charger is a good charger to use for fast charging of car and truck batteries. It provides a good charge rate to fully charge batteries sizes 40 -100 Ah in about 2-5 hours.
Note: Time estimates assume batteries are only discharged to 50% of their capacity
What to Look for in a 15 amp Battery Charger?
Look out for a 15 amp battery charger with an overall positive user feedback. Double-check the user reviews are genuine. Aim for a minimum of 4/5 user rating.
Check that the charger can charge at least the common types of batteries – AGM, Gel, Lithium, or Flooded batteries so that you do not have to buy another charger should you get another battery type.
Can it charge car batteries with extremely low voltages? This is useful when you have to charge a dead battery with a voltage as low as 1 volt or less.
Check that the charger has the auto-shutoff option once the battery is fully charged to prevent overcharging of the battery.
Want to the Best Performance from your 15 amp Charger?
#1. Only connect supported battery types and make sure that the correct mode on the charger that matches the battery type is selected
15 Amp chargers can have various modes depending on which battery type AGM, Flooded, Lithium-ion Phosphate is being charged. Select the correct battery type on the charger that matches your battery type so that your battery is charged as required by the battery manufacturer.
#3. Switch off car accessories (battery installed in the car)
If you are charging the car battery while it is still installed in the car, make sure that all car electronics are switched off to minimize battery drain otherwise the battery will take a longer time to charge or not charge fully.
#4. Still do not leave the charger unattended
Much as the charger may have an auto-shutoff feature, still, monitor the charging process from time to time. Check that the battery is warm to the touch and switch off it if gets hot.
Some chargers abort the charging process when the battery fails to charge within a preset time, probably a sign of a damaged battery that should be replaced. You can catch this early if you are periodically monitoring the process.
Can You Leave a 15 Amp Charger on Your 12 V Battery?
You can leave a good quality 15 amp charger connected to 12V battery if it has the maintain or float feature to shut off when the battery is fully charged.
Only connected recommended battery sizes to the charger, usually 40-50Ah minimum to minimize the risk of overcharging. Consult your charger documentation. In addition, make sure you are applying the guidelines.
Can You Overcharge a 12 V Battery Using a 15 Amp Charger?
Yes, you can overcharge a 12V battery with a 15 amp charger that constantly charges with a peak current of 15 amps regardless of what state of charge your battery is or you connect a smaller battery bank like 10Ah!
Use a good quality 15 amp smart battery charger and maintainer suited to your battery type (AGM, wet, or Lithium) that makes adjustments to the actual voltage and current to avoid overcharging and damage to the battery.
A 15 amp charger will fully charge a 50 Ah car battery that is discharged to 50% of its capacity in about 2 hours. A battery that is drained completely will take considerably a long time to charge.
If you plan to leave the charger connected to the battery, make sure that it has the auto-shutoff feature and that the charger – battery setup is in a well-ventilated environment to minimize the risk of explosions and fire.