12 Volt Lead Acid Battery Replacement

Quick question, I'm trying to understand how my LEAF works more clearly.

Tim mentions an inverter sending voltage to the 12vdc bus? That makes no sense to me, I would expect a DC-DC converter with charging logic.

Can you please clarify, I'm still trying to sort out the charging system on my vehicle.

Additionally, does anyone know of a schematic or diagram of the electrical on these things?

forestrider said:

Quick question, I'm trying to understand how my LEAF works more clearly.

Tim mentions an inverter sending voltage to the 12vdc bus? That makes no sense to me, I would expect a DC-DC converter with charging logic.

Can you please clarify, I'm still trying to sort out the charging system on my vehicle.

Additionally, does anyone know of a schematic or diagram of the electrical on these things?

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I was the one that used the phrase 12v bus.

Doesn't matter to me where it sends it directly because the 12v wiring is all interconnected and any loads are shared between all the devices on the loop.

I'm a computer guy not a electrician or electrical engineer so it may be that I'm using terminology loosely and you can fee free to use the correct terminology from your preferred field of experience. We'll find common ground.

forestrider said:

... I would expect a DC-DC converter with charging logic.

Can you please clarify, I'm still trying to sort out the charging system on my vehicle.
...

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Yes, it has a very strong DC to DC power supply that takes high voltage pack power and produces power to charge the 12V battery. Capable of around 100 amps at 14.4V.

But its charging logic appears to mainly be based on current flow that has been measured by the current monitor in the 12V negative cable, although there are some adjustments based on temperature.

But the current sensor does not see the current drain when the LEAF is Off.
Like the high drain from an OBDII adapter.

And it does not appear to do an adjustment based on voltage like a battery maintainer charging logic.

So depending on use and loads while Off, the LEAF can leave the 12V poorly charged.

Unfortunate it does this.
But for many people using a battery maintainer while the LEAF is Off every week or two is a good practice.

My OBD adapter appears to have drained my 12v down to ~6.9v while I was away last week--enough to kill most functions and get psycho error messages. This is just bad design--if the car needs a 12v computer, the 12v battery should be on the list of critical systems (alongside battery temp an charging timers) that get kept operable.

This is just my $.02 but if your OBD is what killed your 12v battery you have a bad 12v battery. There are other things in the car that consume power as well and a good 12v battery should last a week easy.

I replaced my 12v with the next larger size up and the car has been great, no more low 12v battery lights or dead batteries. The Leaf's 12v charging system seem to work fine with a healthy battery but falls short when the battery starts to fail causing a cascading 12v battery failure. Honestly I think even replacing the stock battery with a average quality same size battery would help a LOT.

http://www.mynissanleaf.com/viewtopic.php?f=9&t=18129&start=20

This is just my $.02 but if your OBD is what killed your 12v battery you have a bad 12v battery. There are other things in the car that consume power as well and a good 12v battery should last a week easy.

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If the battery was chronically undercharged before the trip, this could happen. If the car was plugged in and not charging as well, it would almost certainly happen.

Arlington said:

My OBD adapter appears to have drained my 12v down to ~6.9v while I was away last week--enough to kill most functions and get psycho error messages. This is just bad design--if the car needs a 12v computer, the 12v battery should be on the list of critical systems (alongside battery temp an charging timers) that get kept operable.

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Unless you were measuring the draw on the battery the entire time and have measured what your ODB adapter uses and then have done the math to determine that the ODB adapter is what resulted in the discharge and not the other systems that stay on when the car is off I'm not sure how you were able to determine it was the cause.

It's common enough problem with people that don't have ODB adapters that I think it's likely it would have happened either way.

So Autozone and O'reilly list the 12v battery as a 51R. Does anyone know if that is correct?

Yes the 51R is the stock battery size.

To anyone that has replaced the 12V battery. Did you go through all of the steps the manual calls out? Or, just replace the battery like any conventional car. Pull negative cable first , then positive. Reverse for installing new battery.

rawhog said:

To anyone that has replaced the 12V battery. Did you go through all of the steps the manual calls out? Or, just replace the battery like any conventional car. Pull negative cable first , then positive. Reverse for installing new battery.

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If you're talking about the "wait 5 minutes after shut down before disconnecting 12v", then YES. Otherwise, it's just like replacing any other starter battery.

I just swapped my 12v like normal. I admit I didn't realize there was anything specific we were suppose to do with the Leaf. At the same time I had the stock 12v go completely dead so many times I figured it would be no worse than when that happened.

rawhog said:

To anyone that has replaced the 12V battery. Did you go through all of the steps the manual calls out? Or, just replace the battery like any conventional car. Pull negative cable first , then positive. Reverse for installing new battery.

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Could you elaborate on what the manual calls for on replacement?
I observed the dealer technician replace mine for the second time through the waiting room observation window and I did not observe anything other than standard practice for changing a 12V battery.

When I replaced mine, I hooked a battery charger up to the battery connections, loosened them, removed old battery, connected new one, removed charger cables and done.

great idea.

TimLee said:

rawhog said:

To anyone that has replaced the 12V battery. Did you go through all of the steps the manual calls out? Or, just replace the battery like any conventional car. Pull negative cable first , then positive. Reverse for installing new battery.

Click to expand...

Could you elaborate on what the manual calls for on replacement?
I observed the dealer technician replace mine for the second time through the waiting room observation window and I did not observe anything other than standard practice for changing a 12V battery.

Click to expand...

Look at the manual. There are numerous steps that are referenced from the original item of disconnecting the battery. Some steps involve the Nissan service tool.

jkline said:

When I replaced mine, I hooked a battery charger up to the battery connections, loosened them, removed old battery, connected new one, removed charger cables and done.

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Would it not be dangerous for the Leaf's electronics to go faulty with a high voltage 14.5 upwards charger going into the terminals? I can imagine it with the battery on since that's where the energy is stored and resistance but directly to the cables is quite risky no? My 2011 Leaf's battery shows about 12V with the car off and 12.9X while the car is on. So I figured it's a good time for me to give it a slow 1A charge via my Radio Control (RC) charger that does Pb batteries. It's taking a good charge seems like as it's topping off now at 14.3-14.4V and put in 6aH into it. Still going at this very minute. Hopefully it can keep and hold it's charge once it's fully done.

c4Lvin said:

jkline said:

When I replaced mine, I hooked a battery charger up to the battery connections, loosened them, removed old battery, connected new one, removed charger cables and done.

Click to expand...

Would it not be dangerous for the Leaf's electronics to go faulty with a high voltage 14.5 upwards charger going into the terminals?

Click to expand...

I've seen my Leaf battery go above 14v with Leafspy. I have thought about replacing the stock battery with a li-ion or a lifepo battery, I would build a DIY battery to maximize energy storage. I wouldn't do it for costs, but to improve the quality of the vehicle.

Using a BMS like this, you could create a battery that could be over 2x the capacity of the lead acid battery, with less weight. My Leaf has a solar panel, and I've seen it produce several amps to the battery on a bright day. Realistically the safest would be to go with LifePo cells, 3.2 nominal and 12.8v 4s nominal voltage. This BMS would be ideal. A 3s li-ion bms may work, but that is lower voltages, 12v being max and 11v nominal.

There are also 45-60Ah BMS available but that might be overkill and will cost extra. I've read that you supply current to the BMS, and it will regulate cell charging, including Constant Current charging from lead acid charging methods. This should be safe up to 6 cells in parallel (All in parallel same charge/manufacturer lot). I would look into 15Ah Lifepo Cells, they are 165mm tall, so should fit in an enclosure. But probably not any/many in parallel, there are also 20Ah/30Ah cells available that will fit in the enclosure. I really like what DjDemonD did here.

Quick calculations: you could store 4 in a row (parallel), and 4 in a line (series) in that enclosure, with room for the BMS. Using 16 20Ah cells you could store about 1kwh (16 cells * 20Ah * 3.2v = 1024kwh), or 320Ah. That is almost a 10x increase over the Lead Acid hazard. I run many accessories off of my 12v system so I see many benefits. Though the cost would be almost $500 for all needed parts and cells.

The people who have proactively replaced their 12V batteries after 4 or 5 years are on the right track. Or at the very least, done a battery test. I got a call from my wife a month ago that she was stranded, and the Leaf wouldn't start, and was acting flakey (abnormal panel displays; every light on, and yellow "EV system warning light" on). We tried "jump starting it", but it only barely helped. I had to get the car towed to the Leaf dealership. As soon as they replaced the 12V battery, everything was back to normal. I guess one of the plates got brittle and "fell" onto another, and shorted a cell. That can happen at this age - the car was about 5.6 years old at the point it happened. But the bad thing is that with a regular ICE car, you notice "slow cranking", and get some warning. With the Leaf, you probably won't get any warning before something like this happens, so just know that getting 5 years from a lead acid battery is doing well, and don't wait too long to replace it. The dealer charged $111 for replacing the 51L type battery.

- Bob

Replacing the 12 volt battery every 4 years is generally a good idea, but I and other people with 12 volt system issues experienced problems much sooner. Mine was at just abut 14 months. I still have that same battery, though, and it works fine as long as it gets regular external charges. So just following a timetable for battery replacement will only help those who aren't going to see charging problems.