If you are a DIY sort of person, you have probably already dealt with charging your vehicle’s battery when it goes dead. It is an entirely common problem and one that every driver should know how to handle.
Unfortunately Mother Nature sometimes conspires against us or we might live in a setting where we cannot leave our battery or charger outside on the street; we’ll have to bring it inside.
But is it safe to charge a car battery indoors?
Yes, it generally is, so long as you follow some basic precautions, and use the correct charger with proper settings for your battery.
In-home charging safety protocols are simple and easy to implement, and assuming you’re not attempting to charge in an environmentally sealed room, or charging many batteries at once, you should not have anything to worry about.
As always, recharging powerful batteries and messing with energized equipment warrants a thorough safety briefing. We’ll provide you with tips and other cautionary items below to help you charge your battery inside safely and quickly.
Always Wear Safety Gear when Charging a Car Battery
I know, I know: no one wants to hear this stuff and somehow fewer people ever seem to actually don PPE when interacting with their car battery, but it is smart. Consider that lead-acid batteries (gel batteries or otherwise) contain powerful solutions of sulfuric acid or other acids as electrolyte, and that you will be dealing with some serious amps and potentially high voltage and the need for safety should be apparent.
You should make it a point to always don and properly adjust your safety gear – which should include insulated, chemically resistant gloves, goggles (not mere safety glasses), and other clothing that will protect you from electrical current and chemical splash burns – before you begin any work to charge your car battery.
Does Charging a Car Battery Give Off Fumes?
Yes. When a lead-acid car battery is recharging, it will give off (usually) small amounts of hydrogen gas and other gasses.
In and of itself, this is not dangerous as long as there is proper ventilation; however, if the area in which you are working is not well ventilated, the fumes can become concentrated and pose a risk of explosion or other harm.
Always Ensure Proper Ventilation when Charging
One of the most important items you should consider when charging a car battery inside is ventilation. Using most common chargers on the market, or any charging system with an overcharge feature, your vehicle’s battery will begin emitting a variety of gases.
Among these gases are oxygen, hydrogen sulfide and hydrogen.
It is the latter two in particular that can be dangerous if allowed to build up in quantity, and are responsible for the vast majority of urban legends and legitimate tales of woe resulting from the charging a battery inside.
Luckily, you can mitigate virtually all the danger simply by ensuring that your battery has plenty of ventilation, either by opening a window nearby or just placing it in a drafty room but has plenty of air moving in it.
Failing to follow this safety protocol can result in serious problems and place you, your family members, and pets in danger although this is still highly unlikely.
Hydrogen sulfide is typically produced when a battery is being overcharged, and has a rotten, eggy smell. If allowed to accumulate in sufficient quantities, it can be harmful to people.
Hydrogen sulfide is heavier than air, and sinks toward the floor, making it especially dangerous for pets and children.
Again, the smell is highly noticeable, and if you smell more than the faintest whiff when charging your battery you should discontinue charging and improve ventilation in the room immediately.
Hydrogen is altogether a different problem, though it is a component of hydrogen sulfide gas. Hydrogen is extremely explosive, far lighter than air, odorless and tasteless.
Lucky for us, even when overcharging a battery hydrogen is produced only in tiny quantities, and is so mobile in the air it will take any advantage to escape a room that is not perfectly sealed, and do so quickly.
That being said, it is possible for off-gassing hydrogen to ignite above a charging battery once it reaches as a little as 4% concentration in the air.
Generally, unless you are charging many batteries at once in a tightly sealed room, you will not have to worry about hydrogen gas building up and then exploding your home, but you must remain cautious.
Also keep in mind that both of these gases can negatively affect the furnishings and finishes in your home, particularly fabrics and metals, by discoloring or corroding them.
Place Battery Away from Heat and Open Flame
Never, ever charge your battery near a source of intense heat or open flame. The gasses being released may ignite near open flame and the battery itself will already be warming up due to the charging process, especially if it is charged incorrectly or deliberately overcharged.
Don’t place it near any baseboard, floor or oil heater, fireplace, pilot light, oven, gas burner, stove or near any other heat source.
Is it Safe to Charge a Car Battery in Your Garage?
Yes, so long as adequate ventilation is maintained and proper safety procedures are followed. Aside from ventilation, you will also want to ensure that there is nothing around the battery that could catch fire or react in case of a leak or overheating.
Leaving the battery in the vehicle is best, but if not possible for whatever reason you should clear out a space for it to rest while charging and setup a fan or other ventilation to ensure fumes are not concentrated.
Is it Safe to Charge a Car Battery in Your Basement?
Yes, again, so long as you can ensure adequate venting, something that might not be easy in a basement depending on the age and furnishing of your home. If you must charge your battery in the basement, make sure that it is on a bare floor and as far away from any potential sources of fire as possible.
Can You Charge a Car Battery While it is Sitting on Concrete?
Yes! If there is one admonishment that you will hear routinely on this topic it is that you should never, ever charge a battery while it is sitting on concrete, or store it on concrete after charging.
The reason why usually involves something about the earth or the nature of concrete “robbing” the charge from the battery somehow. Though not true, at least not any more, this used to be good advice.
Sometime ago, car batteries among others were usually encased in rubber or other materials that could allow the electrolyte to seep outward enough to make a conductive path with the concrete itself, discharging the battery in short order.
Turns out there was more than a little truth in this warning!
However, these days our batteries are invariably encased in tough, non-conductive materials (often plastics) that prevent this from happening unless the casing is severely damaged.
So, as long as your battery is of modern make and undamaged you can charge it on concrete with impunity.
What’s more, you should seek to charge and store your batteries on concrete whenever practicable.
Concrete will not burn in case of an accidental fire, is not overly vulnerable to hydrogen gas emitted from the battery and will withstand leaking acid should the battery rupture, making it among the safest surfaces for the task at hand. If you are charging a battery or just storing a spare in your garage, leave it on the concrete without worry.
Keep Kids and Pets Away
If you have little ones and pets, it is imperative that you keep them away from both the battery and the charger while the charging operation is underway.
A battery that is malfunctioning or being overcharged may bubble and fizzle with dangerous chemicals. It could grow painfully hot. The charger’s cables are energized in operation, and any inquisitive pets that try to chew through them will be in for a nasty surprise.
Also anything that knocks over the battery or the charger may rupture them resulting in damage and injury. If you cannot trust your pets or your kids to leave your setup alone you must secure the room where the charging is taking place.
Beware a Short Circuit
You must use the greatest possible care to prevent any metallic object, like a tool, from contacting the terminals of your battery.
This will cause sparks and could potentially weld the tool to the terminals, causing it to become extremely hot and, potentially, slag the terminals themselves.
This can cause a chain reaction if they melt or sag through the casing of the battery for contacting the acids and chemicals within, likely causing an explosion.
Keep the immediate area around your charging operation completely free of all extraneous tools, silverware, wire or anything else that could cause a short circuit.
Use the Right Charger and Right Settings for Your Battery
It is important that you use the right charger with the right settings for your battery. Generally, you do not want to use any charger or charger setting that will automatically overcharge or automatic “desulfate” your battery.
Both processes overheat and dangerously overcharge the battery, not only resulting in a shortened life, but also potentially releasing dangerous quantities of the gases described above.
The best way to charge a battery indoors is with the minimum amount of amperage over the longest possible time. Consult your batteries at specifications and your charger’s manual for details. If you are rushed for time, don’t charge your battery inside.
Don’t Charge Overnight
Or, rather don’t start your recharging operation and then go to sleep or leave it unattended for any extended period of time.
If your battery charger malfunctions, your battery fails or you just accidentally set the charger incorrect will not be awake to arrest the problem.
This could result in dangerous build-ups of gases, fires or potentially even an explosion. Don’t risk it!
Time the recharging operation to coincide with hours when you are awake, alert and able to react quickly to any mishap.
If you are forced to charge the battery overnight, or leave it behind while it is charging, double check the battery, your charger and the charger settings.
Also, don’t do this unless you’re using a smart charger equipped with a “float” or “maintenance” mode that will stop sending charge once the battery has reached its factory prescribed capacity.
A dedicated trickle charger or large battery charger set to trickle charge is also workable.
Charging a car battery indoors is safe so long as some simple procedures are followed and you use the right equipment for the job.
The main concern when charging indoors is properly ventilating the room that the charging is taking place in, keeping the battery away from any open flame or source of heat and keeping inquisitive pets and explorative children away from the battery and the charge.
So long as this is done, you will have little to worry about when charging your vehicle’s battery indoors.
Tom Marlowe practically grew up with a gun in his hand, and has held all kinds of jobs in the gun industry: range safety, sales, instruction and consulting, Tom has the experience to help civilian shooters figure out what will work best for them.