How Long Does it Take to Recharge a Battery?

Have you ever wondered, How long does it take to charge a battery?
In this video, I'm going to show you exactly how to calculate charge time using four different methods: shore power, solar power, alternator, and generator.

Recently, I had a client named Mia who owns a van. She was unsure about how long it would take to recharge her battery using different methods. I walked her through the four main charging options and explained how long each method would take to fully recharge the battery. In this video, I’ll share with you the exact same explanation I gave her.

1. Shore Charging:
First, let's talk about charging the battery with a standard battery charger. Mia has a 12V 200Ah lithium battery in her van. To understand how long it will take to charge, we first need to calculate the battery’s total power storage in watt-hours (Wh): 12.8V×200Ah=2,560Wh

Using a 40-amp charger:
40A×14.6V=584W
2,560Wh÷584W=4.4 hours

So, it would take approximately 4 hours and 24 minutes to recharge Mia’s battery from 0% to 100% using a 40A wall charger.

2. Solar Power:
Next, let’s talk about using solar power to charge the battery. Mia often travels around Nashville and typically gets about 5 sun hours per day. She has 400 watts of solar panels installed on her van's roof.

To calculate the total power harvested in a day:
400W×5 sun hours×0.7=1,400Wh per day

To fully recharge the 2,560Wh battery:
2,560Wh÷1,400Wh=1.8 days

So, it would take almost 2 days to fully recharge Mia’s battery using her current 400W solar panels.

3. Alternator Charging:
Now, let’s discuss using an alternator to charge the battery. Mia’s van is equipped with a 120-amp alternator. To safely charge her battery without overloading the alternator, I recommended using 30% of the alternator’s current, which translates to using a 40-amp DC to DC charger:
14.6V×40A=584W
2,560Wh÷584W=4.4 hours

It would take about 4 hours and 24 minutes of driving to fully recharge Mia’s battery using her van’s alternator with a 40-amp DC to DC charger.

4. Generator Charging:
Finally, let’s talk about using a generator to charge the battery. Mia has a Honda inverter generator rated for 2,200 watts of output power. To optimize fuel efficiency and reduce noise, I recommend running the generator at 70% of its maximum load:
2,200W×0.7=1,540W

Mia’s generator has two AC outputs, allowing her to use two 40-amp shore chargers simultaneously:
584W+584W=1,168W
To fully recharge the 2,560Wh battery:
2,560Wh÷1,168W=2.2 hours

It would take 2 hours and 12 minutes to fully recharge Mia’s battery from 0% to 100% using her generator and two 40-amp shore chargers.

Mia will use a combination of these methods to keep her battery charged. The calculations in this video assume ideal conditions and don’t account for energy losses. In reality, AC to DC conversion efficiency is around 90%, so you might need to factor in a bit more time for charging.

[MarcPugh]

Excellent videos. I am going to be sure to watch all your content. I learn something new every time.

[nelsondog]

I want to install a solar well pump to supply our daily water requirements. The pump will be between 500 and 750 watts but requires 96 volts. What batteries do we need to accomplish this? Any advice on supporting equipment is greatfully appropriated.
I enjoy the format you use to help us understand solar energy. I hope you can use my request in a video example. Thank you and have a nice day. 😊

[charleschimfwembe]

Looks like charging a 12v 100 AH using one 400 Watts solar panel takes far too long to get fully charged. Can't increasing the number of 400 Watts panels, so as to shorten charge time, do?

[E_G]

Do a video on oversized systems; the concept of solar clipping. Emphasize on the myths surrounding it as it relates to hybrid inverters.

I have never heard you mention it in any of your videos.

I have always wondered why hybrid inverter manufacturers, sometimes, state a max pv power input despite the fact oversizing/solar clipping is a safe and common practice as long as one stays within the limits of the charge controller max total voc and max total Isc.

[SqueekyBums]

I was shocked how long the solar panels will take to fully charge the battery.
I have only 240w, 2x 120w panels, and live in the UK. I'm amazed things still work in my van day after day! 😂

[Fatfreddy]

I bought a new ultra lead acid sealed 90ah 12v 760 cc for my 4x4. I can run my 3.5amp fridge overnight through 12v cigarette lighter
10hrs. = 35ah
How long will it take to charge my battery when i start my engine idle in the morning? I'm not sure if the same calculations apply in this case. I have 125amps alternator some say 40min at 1/3 amps of alternator its 3.5L engine Thanks for the great content

[louf]

Video idea:
Spike question: I want to supply a dehumidier (7.5A, 115V). It's power use is ~565W ( ~900VA (.62 power factor)). I have ordered a 2000 Watt Continuous/4000 Watt Peak Pure Sine inverter. Assuming 4x spike allowance, the inverter looks viable, but I'm confused about whether I should have looked at VA (with power factor) or (real) watts. The inverter is advertised with "watts". I measured the dehumidifier running as nameplate says with a Kill-A-Watt.

Also, would adding a run capacitor to the dehumidifier be advisable to increase the power factor to unity, or does the motor need the reactive power component.

[smert_rashistskiy_pederacii]

Nice. And it seems that the car's alternator is the best, simplest and most reliable way to charge the battery.

[RichardwWestmark]

Can discuss whether to bond ground to dc negative or not; we are told to bond common with ground for grid power.

[ImNoExpert]

Great vlog 👏👏👏.. I have been seeing a lot of hype on the New Tesla Powerwall 3.... Could you (briefly) outline the benefits of opting for this unit, versus other multi-bank configurations, together with charging times using solar, wind or other non-polluting charging methods... James

[dendricknonso]

Please create for a 48v battery system 27:09

[DonalldArmentor]

So why didnt you give option of grid charging using 2x 40 amp battery charges like in the generator method as well?

[nasserio]

can you design a solar systems for 2 ton air conditioner running 12 hours a day with ESH=6 hours , off grid and ongrid systems.

[utubeuser]

So what would stop you connecting 2x battery chargers to a power board/strip when wall charging and charging the battery in 2.2 hours like in the generator charging?

[chandramohan-jtmk]

can we hav a video on how much current we can produce on certain much of water wit certain pressure and flow. can car altenator used to charge bateries and converted to ac?

[fransvankralingen]

a 40Amp charger delivers 40Amps, not 584Watts ergo charging time = 5 hours. Ans since there are 2 chargers available in example 4, the same 2 chargers are available in example 1 ergo 2.5 hours

[EPortillo]

Don't know if you already have a video about how to size a solar system. Let´s say a cabin off grid or a shed far enough to be too expensive to just wire it. What values we need to measure to calculate the demand for the system and size panels and battery requirements.

[drumphase_]

Can you explain norminal operating voltage written on some hybrid Inverters ... Do I need to build my solar array up to 240vdc or what? Please explain

[ifell]

Just remember, if using the renogy mppt split charger if it sensors ANY voltage from your solar it halves the alternator current.

[j.davidcox]

I am always confused about how a charger is rated. I currently have a 20 amp charger servicing a 48v battery bank. So, does that mean I have 120v X 20 amps or 2400 watts charging a 48v system? I.e 50 amps DC to the battery? Or does that mean I have a 20mamp DC charge? I believe a 20 amp ac rated charger yields approximately 50 amps DC. Also, I have 4000 watts of solar but I am adding a Lifepo4 system to my current lead acid system. How do I best divert the solar array input from one battery system to the other? I can divert the different batteries going BACK to the inverter but how to divert the array charge current? A simple marine battery switch?