# How much power does it take to start a Leaf from the 12V Battery

### Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

#### knightmb

##### Well-known member
The question has come up before and it can be important when deciding why type of 12V battery you want to purchase if replacing a bad one or just wanting to replace the OEM 12V battery with something better.

The test I did below was on a Gen 2, 2020 Leaf, so these power readings may be more or less depending on the model year. At-least this can give some technical insight and general idea as to how much power is used and what parasitic drains exist between the Leaf being idle and trying to start it.

The first part of the setup is to intercept all the power on the 12V side. The only way to do this is to basically put a meter right into between the power connections to get a direct current measurement. Once I have a current measurement and a voltage reading from the 12V battery, I can do the easy math of V x I = P to get a good estimate on the power usage.

First we start with the battery voltage of the 12V when the Leaf is idle. For mine, idle voltage is 13.25V. I'm using a Lithium, not a Lead Acid OEM, so the resting voltage is going to be higher, but this won't affect our calculations for power usage.

Next I measure the resting current, in this case, mine was showing 0.126 A, which works out to 0.126 x 13.25 = 1.67 Watts of power. So the Leaf just sitting around doing nothing (no Cell communication for example), the Leaf is consuming about 1.67 watts of power from the 12V battery system.

Next, measure current when you step into the Leaf, sit down and put your feet on the Brake pedal right before you turn on the Leaf. As you can see, just doing all that already uses 3.321 Amps of current, even before I turn it on. So that works out to 3.321 x 13.0 = 43.2 watts of power. Why am I using 13.0 volts? Because the voltage goes down on the battery when you increase the load current. I only have one camera, so trying to get a picture of all the meters at once was beyond my single ability. I had to eyeball it while taking the picture and make note.

Finally, pressing the Start button on the Leaf, final picture shows the current used. 13.7 amps of current at 12.8 volts, that works out to 13.7 x 12.8 = 175.4 watts of power to start the Leaf. Now because just pressing the brake pedal in with the computer on uses 43.2 watts of power, we can figure that it probably takes about 175.4 - 43.2 = 132.2 watts of power to power up the main battery relays and have it take over the powering the entire Leaf. But...we can't get around starting the Leaf without having the brake pedal pressed in, so it makes sense to roll all that power into one reading since that is the peak the 12V battery is going to need to produce just to turn on the Leaf.

Hopefully this will answer my and your own question of curiosity about power usage on the 12V side of the Leaf.

Great test, thanks for sharing the data.

When the car is OFF and just sitting there, then it is pulling about 3 AHr per day, so the typical lead acid battery will be drained dead in about 10 to 14 days.

This is really helpful, as it confirms my hunch that a Noco GB20 jump starter is more than adequate to jump start a LEAF. Thanks!

I already own a 12V LIPO pack that I use for spot welding. For any of the experts out there, can I DIY retrofit the LIPO pack to act as a jump starter? I would imagine they use some diodes to ensure current only flows one way. What other protections would be needed, to safely use a LIPO pack for jump starting?

knightmb said:
The question has come up before and it can be important when deciding why type of 12V battery you want to purchase if replacing a bad one or just wanting to replace the OEM 12V battery with something better.

The test I did below was on a Gen 2, 2020 Leaf, so these power readings may be more or less depending on the model year. At-least this can give some technical insight and general idea as to how much power is used and what parasitic drains exist between the Leaf being idle and trying to start it.

The first part of the setup is to intercept all the power on the 12V side. The only way to do this is to basically put a meter right into between the power connections to get a direct current measurement. Once I have a current measurement and a voltage reading from the 12V battery, I can do the easy math of V x I = P to get a good estimate on the power usage.

First we start with the battery voltage of the 12V when the Leaf is idle. For mine, idle voltage is 13.25V. I'm using a Lithium, not a Lead Acid OEM, so the resting voltage is going to be higher, but this won't affect our calculations for power usage.

Next I measure the resting current, in this case, mine was showing 0.126 A, which works out to 0.126 x 13.25 = 1.67 Watts of power. So the Leaf just sitting around doing nothing (no Cell communication for example), the Leaf is consuming about 1.67 watts of power from the 12V battery system.

Most vehicles, including my Leafs, typically draw about 60ma or less when the system ECUs enter their sleep modes.

knightmb said:
Next, measure current when you step into the Leaf, sit down and put your feet on the Brake pedal right before you turn on the Leaf. As you can see, just doing all that already uses 3.321 Amps of current, even before I turn it on. So that works out to 3.321 x 13.0 = 43.2 watts of power. Why am I using 13.0 volts? Because the voltage goes down on the battery when you increase the load current. I only have one camera, so trying to get a picture of all the meters at once was beyond my single ability. I had to eyeball it while taking the picture and make note.

You need to check whether pushing the brake pedal turns on the brake ECU without running brake pump test, as happens once the vehicle enters the run mode.

knightmb said:
Finally, pressing the Start button on the Leaf, final picture shows the current used. 13.7 amps of current at 12.8 volts, that works out to 13.7 x 12.8 = 175.4 watts of power to start the Leaf. Now because just pressing the brake pedal in with the computer on uses 43.2 watts of power, we can figure that it probably takes about 175.4 - 43.2 = 132.2 watts of power to power up the main battery relays and have it take over the powering the entire Leaf. But...we can't get around starting the Leaf without having the brake pedal pressed in, so it makes sense to roll all that power into one reading since that is the peak the 12V battery is going to need to produce just to turn on the Leaf.

Once the vehicle is in the run mode, most all the vehicles ECUs are in their powered-up mode, and thereby consuming current supplemented
by the Li-Ion battery via the HV converter.

nlspace said:
Great test, thanks for sharing the data.

When the car is OFF and just sitting there, then it is pulling about 3 AHr per day, so the typical lead acid battery will be drained dead in about 10 to 14 days.

Remember, the BMS monitors the 12V voltage and uses the Li-ion battery to periodically charge the 12V battery via the HV converter.

Remember, the BMS monitors the 12V voltage and uses the Li-ion battery to periodically charge the 12V battery via the HV converter.

Ideally, anyway. If that worked as well as it should, we'd have 10,000 fewer posts here.

I think that I was remembering 10 amps in the context of what people - including me, IIRC - were using, capacity-wise, as emergency jump-starters. A 10AH SLA UPS type battery would likely provide a 1.5C discharge rate at least briefly.

lorenfb said:
You need to check whether pushing the brake pedal turns on the brake ECU without running brake pump test, as happens once the vehicle enters the run mode.
It is probably a Gen 2 thing, but I noticed that my key fob activates the computer when I get in before even pressing the brake pedal as the screen comes on to show you the mileage and stuff on the dash. I didn't mention it above, because I couldn't find a way to stop it from doing that and still be able to start the Leaf. I don't remember my Gen 1 Leaf doing this, so it's probable the power usage is much less in the Gen 1 models when turning on the EV. On mine, it took about 2 minutes after shutting it off for the power usage to drop down to the lowest level, it might have a deeper sleep mode perhaps, but the longest I waited after shutdown was about 30 minutes and the power draw stayed the same. I could repeat the same experiment on my wife's 2018 but she gets nervous when I start messing with her Leaf. :lol:

I did take a picture of the current usage without the brake pedal, just sitting in the car doing nothing, so here is that reading picture. Glad I didn't delete the picture or voltage notes (13.1v when computer active), wasn't sure if it was useful data, but here it is.
2.576 x 13.1 = 33.75 watts just sitting in the car. I think technically the cabin lights are also part of the power reading shown here.

nlspace said:
Great test, thanks for sharing the data.

When the car is OFF and just sitting there, then it is pulling about 3 AHr per day, so the typical lead acid battery will be drained dead in about 10 to 14 days.

I have not had the chance to do the math on the daily power usage, so thanks for doing that.
So, for reference, my wife's 12V OEM battery, which was over +3 years old before I changed it out, could only manage 6 AH during my discharge testing. That as in warm indoor temperatures, so I don't think her battery would have survived the winter this year if I hadn't done the upgrade for her; colder weather was coming soon. I don't know how often the Leaf tops off the battery, but in her case, half it's capacity would be draining daily if she wasn't driving frequently.

This is the video I made on her battery a while back. Beforehand I didn't know how much power it took to actually turn on the Leaf, but her battery was struggling just to push out +160 watts before it hit the 10 volt range. It would really struggle with the +175 watts needed to actually turn on her Leaf I'm guessing. Her Leaf does the same thing, the computer on the dash comes on as soon as you get into it.

Good info -- thanks !

Pickle Rick--What is the capacity of your Li starter battery?

Good that you saved that last data--using two loaded tests data can calculate the internal resistance of the Li battery, about 27 mOhms. Seems typical for Li so it is in good shape.

The label on your wife's battery indicates capacity of 43 Ah at C/20 or 2.1 Amps load, so if you measured it at 6Ah then it was worn out and time for a new one for sure.

alozzy said:
I already own a 12V LIPO pack that I use for spot welding. For any of the experts out there, can I DIY retrofit the LIPO pack to act as a jump starter? I would imagine they use some diodes to ensure current only flows one way. What other protections would be needed, to safely use a LIPO pack for jump starting?

I wouldn't really worry about using diodes unless you plan on trying to jump your Leaf with your jump battery being dead, power should always flow from the jump starter to the Leafs battery. My only worry and maybe it might not be a issue is if your jump starter is large and capable of putting out a large burst of current, as Li batteries generally are, would the surge of power from your jump starter to Leaf be enough to cause issues with something? for example melting your jump-starting wire, etc. Maybe I'm being a worry wort but I'd more worry about that than a diode to keep power from flowing from your Leaf to your jump-starter.
O.P. thanks for all the tests, it's the thing I love to do but generally never have enough time
The one thing I'd like to know and someone else mentioned it earlier would be the true deep-sleep parasitic amp draw. Say hook up your amp meter and take a reading a couple of hours later, as someone else mentioned I bet it would be far less than the .xx amps you saw after only a short time.

jjeff said:
The one thing I'd like to know and someone else mentioned it earlier would be the true deep-sleep parasitic amp draw. Say hook up your amp meter and take a reading a couple of hours later, as someone else mentioned I bet it would be far less than the .xx amps you saw after only a short time.
I'm doing that test right now actually. The weather today is a very warm "global climate change" 73 F here today (should be around 50F instead normally). Once a few hours pass, I'll post up the results along with some more testing on my wife's 2018 while she was out shopping and didn't know I was experimenting on her Leaf. :twisted:

Great, the wife is out for a while and left her Leaf here, what is a husband to do? Why, take it all apart and experiment, then try to put it all back to together before she gets back, all in the name of science! :twisted:

I'll summarize everything here since this is identical to what I did on my 2020 Leaf.

First image, how much current is used stepping into the car *without* pressing the brake pedal. Battery voltages were near identical (we have the same brand/capacity Lithium 12V battery, so makes sense). The first difference I noticed was her 2018 Leaf current draw was higher than mine, it shows 3.153 A vs. my 2.576 A. I had to scratch my head a little until I figured out, she still has her "incandescent" cabin lights and mine are all LED, so my lights draw less power with the door open. Her power draw is 3.153 x 13.06 = 41.18 watts, that's 7.43 more watts than mine, but I suspect the lighting is what is making that small difference.

Second image, how much current is used when the brake pedal is pressed in, right before hitting the start button. This image showed around 3.922 amps, which is still higher than my 2020 Leaf, which measures around 3.321 amps doing the same thing. Again, I suspect the LED vs. incandescent lighting is the power difference. So her 2018 Leaf is using around 3.922 x 12.96 = 50.8 watts of power versus my 43.2 watts of power to do the same thing.

Finally, third image, how much current to start the 2018 Leaf, meter was reading 14.45 A peak with a voltage of 12.79, works out to 14.45 x 12.79 = 184.82 watts of power to start a 2018 Leaf. My 2020 Leaf does the same thing with 175.4 watts, but again, I suspect it's the LED lighting that is making that slight power difference.

And now the interesting part, how much parasitic power draw does the Leaf have during a deep sleep. It appears to be kind of random when it will happen on a Leaf because on my 2020 I didn't wait long enough. But on my wife's 2018, I only needed to wait about 15 minutes for it to finally hit deep sleep. The picture below shows the measurement, only 0.012 A with a voltage reading of 13.19, that works out to a tiny 0.012 x 13.19 = 0.158 watts of power. I suspect my 2020 would be similar once it finally hits deep sleep, I just didn't wait long enough or some background process (maybe the Nissan telematics services) might have still been running? Either way, it appears for the Gen 2, power usage is very similar from 2018 to 2020 anyway, I suspect 2021 and 2022 would probably be similar minus any radical design changes.

I was able to get everything put back together and buttoned up before my wife got back, so one day she will probably find out as she does occasionally read these forums, but I'm going for forgiveness instead of the permission response. :mrgreen:

would a clamp on DC ammeter work to measure this? could use peak mode?

Learjet said:
would a clamp on DC ammeter work to measure this? could use peak mode?
I don't believe they make a clamp-on DC ammeter, I believe they are all AC as AC generates the EFM that the clamp on meter reads, I could stand to be corrected though I personally have only seen in-line DC ammeters.

Learjet said:
would a clamp on DC ammeter work to measure this? could use peak mode?

You can, but I find that when dealing with currents below 1 amp they are highly inaccurate unless you spend a lot of money for a very expensive one that is sensitive enough. I'm measuring currents down to the thousandth of an amp, so I don't know of any DC clamp on meters that good.

jjeff said:
Learjet said:
would a clamp on DC ammeter work to measure this? could use peak mode?
I don't believe they make a clamp-on DC ammeter, I believe they are all AC as AC generates the EFM that the clamp on meter reads, I could stand to be corrected though I personally have only seen in-line DC ammeters.

I have one seems to work ok. Also, I have a DC ammeter in my RV that use a coil over the wire vs. a shunt....hall effect I believe its called?

knightmb said:
Learjet said:
would a clamp on DC ammeter work to measure this? could use peak mode?

You can, but I find that when dealing currents below 10 amp they are highly inaccurate unless you spend a lot of money for a very expensive one that is sensitive enough. I'm measuring currents down to the thousandth of an amp, so I don't know of any DC clamp on meters that are that good.

makes sense.

Thanks for posting the data!
I have been using a 20 AHr Lithium starter battery for almost 8 years now (you can search my name for the thread), and at one point determined I could "start" my Gen1 Leaf with about 12 V @ 10 AHr. The larger "stock" lead-acid starter batteries they put in EVs are definitely overkill, but it's probably easier to use something already spec'd for their smaller ICE vehicles (although LiFePO4 starter batteries and EVs are a match made in heaven).