Lead accessory battery replacement issues

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groingo

Active member
Joined
Mar 4, 2017
Messages
30
Replaced my leaded accessory battery with Ohmmu Lithium Ion replacement accessory battery for my 2014 Leaf but it doesn't work, nothing....took three Lifep04 chargers before I found one that could charge the battery....looks like the new battery has BMS issues, anyone else tried one of these?
 
My buddy replaced the SLA battery in his Tesla Model S with one of those and is extremely happy with it.
We replaced the SLA in our Electric smart car with a LiFePO4 from China almost a year ago and have had
zero problems with it. I plan to do a preemptive replacement with another one in the 2019 Leaf in about a year.
 
Did you measure the voltage when you got it? My guess is that it was below the voltage at which most lithium chargers will recognize that they are connected to a battery. If this is the case, then it may be ok, but equally likely it is damaged.
 
Voltage before charge was 13.1 volts, when charge was complete it was 14.2 and an hour later settled to 13.80 which is normal but I do know when a BMS is involved there needs to be a handshake between battery and car and charge as well, I suspect bum software in the BMS.
 
groingo said:
Voltage before charge was 13.1 volts, when charge was complete it was 14.2 and an hour later settled to 13.80 which is normal but I do know when a BMS is involved there needs to be a handshake between battery and car and charge as well, I suspect bum software in the BMS.

With the 12V Lithium I've dealt with, the BMS is simply there to protect the battery from over-charge, over-discharge and over-current, that's about it. The Leaf does no communication with the 12V battery through the connectors, the BMS in the 12V works independent of the outside.

What the Leaf does need though, is a minute to boot up after you connect the power. You'll see a big spark when you connect it because it is charging up the computer capacitor. If the car alarm didn't sound the moment you connected power, that's a good sign. After a minute, get into the car and see if you can at least start ACC mode, then try Full Display Mode before trying to start it. If you get through the first two battery modes but can't get it to start, probably means the 12V Lithium can't put out the surge power needed to engage the relays for the mains.

I have a good idea how much power it takes to start a Leaf, but I don't know what the "minimum" battery capacity/size is to also do this. :?
 
LiFePo4 batteries tend to have a lowish C (discharge measured as multiples of the total capacity) rate, but even if it were just 1C, a 15AH battery would suffice to start a Leaf - especially a freshly charged one. I suspect that the battery is no good, or was damaged by being shipped with less than 10% charge. It may read high enough but have little actual capacity.
 
LeftieBiker said:
LiFePo4 batteries tend to have a lowish C (discharge measured as multiples of the total capacity) rate, but even if it were just 1C, a 15AH battery would suffice to start a Leaf - especially a freshly charged one. I suspect that the battery is no good, or was damaged by being shipped with less than 10% charge. It may read high enough but have little actual capacity.

Ohmmu's replacement for Nissan LEAF claims a true 40AH capacity. Internal protection could be tripping under load, but its unclear at this point whether the car can start at all?
 
An Amp meter would be helpful here.

I suggest leaving the 12v in your home for a day to warm up, then see if it works in the LEAF. That won't help you use it in the winter, but it will tell you what the problem is.
 
groingo said:
Voltage before charge was 13.1 volts, when charge was complete it was 14.2 and an hour later settled to 13.80 which is normal but I do know when a BMS is involved there needs to be a handshake between battery and car and charge as well, I suspect bum software in the BMS.
Actually, any "settling" over ~13.3v is not normal for a LiFePO4 starter replacement battery. Not to state the obvious, but Lithium batteries don't act like lead acid, although (when properly designed) they make great 12v replacements.
For the record, I've never heard of Ohmmu, and suspect the battery was "bad" from the start.
 
LiFePo4 batteries do run that high right after charging (they drop back after that), and I don't see how that could be changed, unless the starting batteries are kept at ~90% of capacity for longevity, which seems likely and prudent... Looking at my LiFePo4 SOC chart, I see both 14.4V and 13.6V listed for 100%, 13.3v is 90%, and 13.1V is 40%. So if that battery read 13.1 before charging, it was shipped at a safe 40% and charged up properly.
 
I would suspect a bad battery, we have a good idea about how much power it takes to start one via this: https://mynissanleaf.com/viewtopic.php?f=9&t=32820
So, if the battery can't produce +185 watts of power without the voltage dying, it's not going to work regardless of the voltage level when fully charged. :(
 
LeftieBiker said:
13.3v is 90%, and 13.1V is 40%.
Trying to figure out SoC of an LFP battery from just voltage is like reading tea leaves. The voltage versus SoC is quite flat except at the extremes, it depends on temperature and load, there is hysteresis, and more. LFP is different to pretty much every other Lithium Ion chemistry in that respect.
 
lebikerboy said:
As previously stated that I would, I did order a LFP replacement battery as my warranty had expired. I'll report how it goes when I receive it...

Received the battery yesterday and installed today. All went well and zero electrical problems with the new battery. I swear the car runs better... ;)
 
lebikerboy said:
lebikerboy said:
As previously stated that I would, I did order a LFP replacement battery as my warranty had expired. I'll report how it goes when I receive it...

Received the battery yesterday and installed today. All went well and zero electrical problems with the new battery. I swear the car runs better... ;)
I'm curious what brand you bought? Might be good info since there are some new LiFePO4 vendors out there.
 
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