12v Battery - All You Ever Wanted To Know

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I have a question about the 12v plug in accessory outlet on my iMiev. Does it run off the little battery
only, or does it draw power from the main battery? I have a backup battery --ecoflow -- for when the power goes off in the house, and I am wondering if I could use the car to top up that battery if need be? I suppose it could work if the outlet in the car draws from the main battery but not from the 12v little battery only. Any help on this is appreciated! Roger in Halifax [email protected]
Hi Roger

The 12V outlet is powered by aux battery, however when the car is in Ready/charging the aux battery itself is charged by the traction battery via OBC.

While that would work for you in principle the output is only rated at 120W, (less than 10A). Even if you connect straight to the battery terminals I doubt that the OBC power rating is sufficient for your purposes.

If you’re determined, it is possible to tap into the CHAdeMO port and run the house directly from the big battery using a solar inverter.

I tried to start our iMiev the other day and nothing happened. So I removed the 12v and took it to Autozone and after testing it, the clerk there pronounced it dead and quoted me around $200 for a new battery ( 151R3xt ). Rather than pursue this option, I chose to look at the NOCO NLP30 battery ( https://no.co/nlp30 ) discussed in this thread/topic, but found a battery charger also. After chatting with NOCO support, I bought the NOCO Genius 10 ( https://no.co/genius10 ), which NOCO said would bring a dead battery back to life, including if the battery had sulfation. I bought it for the $99+ sale price.

Upon receipt I plugged it in and began charging the battery; after 5-6 hours or so, the Genius 10 green light came on indicating charging completion and success. After reinstalling it, the iMiev started right up. No "problemo" and no error codes!

Following JoeS's advice regarding his Meanwell tender ( https://myimiev.com/forum/viewtopic.php?p=46256#p46256 ), I will probably buy this battery tender ( https://no.co/genius2d ) or something like it to keep the 12v in shape and avoid buying a new battery for a while.

Our 12v battery was just less than 2 years old and purchased from the dealer, now Bell Road Mitsubishi. My belief is that the 31 days of record heat in Phoenix ( https://www.cnbc.com/2023/08/01/phoenix-sets-record-of-31-straight-days-of-110-degree-temps.html ) caused or contributed its demise. During that period, we also had to charge the vehicle on several occasions, which I am sure didn't help the 12v either.

In any event, our iMiev is back in business.
Edit: I had incorrectly read Phximiev's entry (above) as his having actually bought a NOCO NLP30 battery, and my writing below reflects that. I'm leaving my discussion as it is still applicable in case anyone is considering installing a "12v" LiFePO4 battery into the i-MiEV (remember, from previous discussions, the concerns are low-temperature operation). Phximiev's subsequent post clarifies his situation and emphasizes being aware of upper temperature limits when buying 12v chargers.
Phximiev, that battery was sure easy to manhandle into position, wasn't it! :D

It'll be interesting how well your NOCO battery works out, as mine is still performing its daily duties flawlessly. Remember, the battery has a very low capacity which can be easily depleted if the car's dc-dc is turned off (i.e., not in READY) and using accessories such as the radio.

I use the small Meanwell power supply (set to 13.6vdc) whenever the car isn't going to be driven for 4 days or more, as that takes care of the car's vampire load while holding the battery at a nice float voltage. Here's the Meanwell I use:
Maybe in your high temperatures you might reduce the voltage to 13.3vdc, which is typically the voltage my NOCO battery eventually drops down to when I disconnect my power supply.

The smaller NOCO chargers (I'd go with the 1A although why not just use the 10A?) might not be suitable for our in-car float charging (maintaining) application as I don't know at what voltage it settles down to in this float application with a car's vampire load drawing away some current.

The NOCO Genius 10 is a very good multi-purpose charger. In general, I don't know how chargers will react when having to deal with the car's vampire load as I would hope they don't raise the voltage trying to compensate. Since you already bought the NOCO Genius 10, you might put a voltmeter on it and see if the voltage drops to 13.3-13.6v or if it tries keeping your NOCO battery at 14.6v. The user guide doesn't tell us, nor do the specs. I'm personally not comfortable with keeping a LiFePO4 battery floating at 14.6v as that is typically, for four cells in series, the absolute maximum voltage per cell. Yes, the NOCO battery has a built-in BMS which should keep the cells happy, but...

When in READY, at normal room ambient temperatures our i-MiEV dc-dc puts out 14.4vdc. I haven't paid attention to see how much (if at all) that voltage drops at high ambient temperatures.

Oh, and make sure the voltmeter you are using is calibrated. Lead-acid batteries are very forgiving whereas other chemistries aren't.
There are some key differences between the battery maintainers. Additionally, given that I live in Phoenix where the temperatures are routinely over 104 degrees, the selected battery maintainer must operate over 104 degrees.

Per their website, the Genius 2d ( https://no.co/genius2d ) operates from "-4°F to +140°F (-20°C to +60°C)" and with "all types of 12-volt lead-acid batteries, including flooded, gel, AGM and other maintenance-free batteries." But not lithium-ion batteries apparently. This would work just fine with the Mitsubishi battery that I repaired/recharged and reinstalled in the car.

The Genius 1 ( https://no.co/genius1 ) operates from "-4° to 104° F (-20° to +40° C)" and with "flooded, gel, AGM, and maintenance-free, plus lithium-ion batteries." So this apparently won't work as a maintainer in Phoenix because of the operating temperature limitations.

I have an email to NOCO about these questions and should hear back next week.

The NOCO Genius 10 ( https://no.co/genius10 ), which I bought, handles "flooded, gel, AGM, and maintenance-free, plus lithium-ion batteries" and operates from "-4° to 104° F (-20° to +40° C)" and does battery maintenance as well as desulfation. Given the state of the Mitsubishi battery and the comments from the clerk at AutoZone, I thought the battery needed a boost/repair and possibly desulfation, hence my decision to purchase the Genius 10. Also, since I had already removed the battery, I charged the battery indoors where it was cool, so no issue with the operating temperature. This charger/maintainer would allow me to repair and maintain any battery that I acquire in the future as long as I remove it from the car. I do believe that I could mount it in the car as a maintainer, but for the operating temperature limitation.

I'll post an update once I hear back from NOCO next week.
Phximiev, excellent point about paying attention to the upper temperature operating limits of not just chargers but all equipment used outdoors in your terribly-hot summers.

I corrected my previous writeup (above) as I had incorrectly read what you properly wrote and thought you had actually purchased a NOCO NLP30 battery.
Per NOCO, all of their chargers simply stop working when the temperature is outside their limits and begin working again when they are within the limits.

The Genius 2d has an upper operating limit of 140F degrees (and a lower of -4F degrees) but cannot handle lithium batteries. In warmer climates, this may be a good battery maintainer for the Mitsubishi batteries and, given KIEV's thoughts about one of the causes of OBC failures being a defective battery, perhaps essential to avoiding an OBC failure.

The NLP30 lithium ion battery has an operating limit of -4F degrees to 140F degrees. If the Mitsubishi battery fails, this is probably a good replacement option in warmer climates.
Here is a bluetooth-connected recording 12v battery monitor that is excellent for measuring and tracking our 12v battery. Unlike other relatively-inexpensive instruments, this one has proven to be quite accurate. I use it with an iPhone. I learned about it on the Kona Electric forum where that car's 12v battery and its 12v BMS are notorious. Been using it for over a year in various vehicles and static solar battery inverter applications. Display duration is selectable at one day, seven days, or fifteen days. There is a 30-day timeframe limit but it is only for updating the data as much longer durations are stored on the phone (I think). Select whether you want the lead-acid (first link) or lithium (second link) version:

These are called BM2, seemingly identical with other manufacturer's labels, but I had bought a Quicklynks which is very accurate and I recently bought a second one specifically for 12v lithium batteries (same price) but it appears no different than the other one for measuring as all it does is alter the warnings based on LiFePO4 voltages instead of lead-acid.

The following two screenshots show a continuum - the first part of the graph is the monitor attached to my wife's i-MiEV (Moto) and an older flooded lead-acid battery (note how it sags) whereas the second (more-recent) part of the graph (starting on 22 March) is of my Mitti with the NOCO lightweight LiFePO4 battery. Moving a finger across the graph shows readings at any point on the graph. Caution: note the ridiculous non-linearity in the scale in the upper portion of the graph - I had hoped that this would have been fixed in this new (lithium) version of the app. Hmm, I forgot to take an upper voltage reading screenshot.

The voltage accuracy is within the 10mv that one sees on the reading, which is certainly close enough for our purpose. It's rare that I recommend a product, but I think this is useful in so many applications. I wish they had a current (amps) version of this thing.


that's a great find Joe, Amz has a suggestion for one with current sensing on the same web page, no idea of its accuracy


OT: am looking for similar function 120/240AC monitor (with BT not wifi)