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Ohmmu 12V Battery Feedback
- Thread starter LasVegas2019
- Start date
daniloreyes
Member
I have to ask... with the V4+ still have the issue, how is this better? Is there a process to remove the errors on the car with it?
Technically clearing the error codes is done by the reset. That requires as far as I'm aware anyway disconnecting the dc/dc contactor under the rear seat and then disconnecting the battery and then reconnecting both of those after a short delay. There are some reports that you can clear errors and do a full 12 volt reset solely by disconnecting battery but I do not believe that is the case.
I installed an Ohmmu battery in my 2013 Model S P85 a couple of years ago. So far I have not had a single issue with it. I'm guessing all of these issues are with the newer vehicles that have more advanced 12V battery charge controllers. I got sick and tired of replacing the AGM battery in my 2013 every couple of years, especially since it seems Tesla went out of their way to make replacement difficult. It's really buried under a lot of stuff in my 2013 and not a simple 15-minute replacement operation. To get to the 12V battery on my car, the frunk must be removed, as well as a strut, a fuse box unbolted, the cowling loosened up, and a lot of trying to shoehorn it out. Just removing the nut on the bolt holding it in place was very awkward and left me sore. The Ohmmu battery, being as light as it was, was much easier to install than removing the AGM battery. I hope it lasts at least 4 years, preferably longer. I also installed it because when I go camping I wired in a 12V always-on outlet to power a refrigerator which increases the cycling of the battery. If replacing the battery on my car were not so awkward and time-consuming I probably would not have bothered with the Ohmmu.
I don't have a Ohmmu, but I saw this the other day. Go to 5:07. Just an fyi.
Sadly that video is a mix of the usual good and dis- information or at least some correct and valuable stuff with some stuff that's misleading. What he fails to mention is that these types of batteries work without incident in virtually every other car and in the Model S and X and only the different charging routines on the Model 3 and Y instituted only since the fall of 2021 appear to have generated significant incompatibility.
There are a lot of posts and a fair amount of confusion about what that incompatibility consists of, but the fact that this type of battery has worked flawlessly on dozens of ICE vehicles and on the Model S and X suggests that the problem is not the battery but an incompatibility with Tesla's revised 12 volt subroutines.
It is worth also emphasizing that this incompatibility emerged after Tesla received a boatload of flack about the poor longevity of 12 volt batteries in their cars. We believe that has led to the installation of desulfation routines which are not consistent with lfp chemistry.
There are a lot of posts and a fair amount of confusion about what that incompatibility consists of, but the fact that this type of battery has worked flawlessly on dozens of ICE vehicles and on the Model S and X suggests that the problem is not the battery but an incompatibility with Tesla's revised 12 volt subroutines.
It is worth also emphasizing that this incompatibility emerged after Tesla received a boatload of flack about the poor longevity of 12 volt batteries in their cars. We believe that has led to the installation of desulfation routines which are not consistent with lfp chemistry.
Temperature was the issue I had. After observing charging routines with battery monitors and then with the updated service mode, I noted the V4+ worked flawlessly for about 10 weeks until the temperatures dropped below 40F. Near 30 I got the replace battery message. Pulled the battery and tried charging at 1 amp at below 40F and would not take charge. Increasing to 6 amps charged to 100%.
The latest charging routine I observed would do a high draw (25-30 amps) on startup, then charge at 25 amps briefly then dial down until fully charged to about 14.7 volts. Then the battery would have shallow draw down until about 13.4 volts and zero draw. Float voltage would be +/- 01-.04 amps. If cold, the battery would not take the charge and there was the failure message.
Put the battery back in at warmer temps and worked normally. Ohmmu has a software update due out next month to address this that will be updatable from the app. Future models will have silicone heating mats between cells but they have indicated they are not really necessary. I suppose you would want that if living in -25F and below climates like upper midwest and Canada. But at those temperatures even a lead acid would be problematic.
What he doesn't fail to mention is that the Ohmmu has no temperature sensing, the BMS allows charge beyond the cell specs, and that the company is not transparent with the capacity of the battery. None of these have to do with Tesla's changes.
So? That doesn't make the Ohmmu a good solution for a Tesla. That proves it's a bad solution, which is all Ingineerix was saying. Just because no other car has desulfation doesn't mean it's bad for Tesla to have it.
It's continuously amazing that as Ohmmu fights all the issues they have, the bad PR, and the existential threat caused by Tesla's own LiIon in newer cars, that they rely on some guy on a forum to communicate the improvements to their product. But it's hilarious that they would say they don't need heating mats when their current product already shuts off at 30F (which itself is an improvement to no sensing at all). But why are they adding heating mats if they aren't needed? The cells can't charge below 30F. Why would this only be an issue at -25F?
There is zero issues with a lead acid at -25F. This is not a cranking battery. A lead acid still has ~25% capacity at -25F, and the worst that happens is the car has to wake more often to charge it. Meanwhile the LFP battery completely shut of 55F earlier.
What are people trying to achieve by buying an Ohmmu today? It has way more problems than a Lead Acid and costs more over time to boot.
They paid off a lot of "influencers" to make videos convincing viewers to make this expensive and silly purchase.
This makes a lot of sense as I have noticed that I'm more prone to difficulties when it's colder and also when the car has been sitting for quite a while. I do not have the most updated version of the battery however
I noticed this as well. All research into the Ohmmu battery problems only seems to happen with Model 3 and Model Y cars after Tesla added some additional checks due to the horrible reliability of AGM batteries. Also, LFP batteries are more tolerant of charging at low temperatures. My experience with AGM batteries with my 2013 Model S has been abysmal and I have zero regrets for making the change to the Ohmmu battery if I get at least 4 years out of it, preferably more.
I'm now curious as to how their BMS works since I have designed a few BMS systems although I by no means consider myself an expert.
There is a few reasons why people want to still buy these batteries or use them.
- Freedom of choice, tesla should allow people to use parts they want to use. They bought the car, its theirs to do with what they please. It comes down to right to repair and having tesla dictate how their cars are repaired and who can repair them and with that parts. Be like ford saying only ford 12v batteries can be used in their ICE cars, any other batteries will be detected by the cars computer and disable the vehicle.
- Marginal weight savings, every bit counts in a EV? Cant think of anything easier then removing lead from an EV to lose some weight.
- Modding, some people like to customize and mod their cars. Me coming from a 2015 mustang i used to love to tweak and improve the performance of my car. Thats very hard to do if not impossible with a tesla. So only thing we have is some exterior parts and suspension you can adjust. A 12v battery isnt a supercharger, but its something?
BS. Any Group 51R battery will fit. For example: https://www.napaonline.com/en/p/BAT9851RT
Thing is this -- Tesla obviously does a big volume with Atlas BX (Hankook) for batteries, and they're selling them to us at a ridiculously good price. Why would you pay more anywhere else?
Tesla's model isn't to use service as a gigantic profit center, so we get the benefit of their volume agreements with Hankook.
The Ohmmu is 9.2lbs lighter than the factory battery. Take one good dump and you're there. 9.2lb is so insignificant the only place you'd notice it is in your mind.
Difficult for the sake of being different. Got it. That's actually the most rational reason I've heard yet.
This is like saying that BMW should support you running diesel in your M5, Ford should allow you to just drop in larger injectors, or Tesla should support you replacing the battery coolant with milk. Yeah, they share similar properties, but....
A LFP battery flat out isn't a lead acid battery no matter what the vendor tells you. It's incompatible with the car's design. It physically works differently. Why do you expect it to work?
Even with stuff that does fit... When you put coilovers on your mustang and they rattle, do you complain to Ford, or Roush?
Quite the reverse in an EV. The car is already 4K lbs. Taking out 10lbs is 0.25%. Meanwhile, in a 3K lb ICE car, you generally have larger batteries so you can save 30 lbs. That's 1%.
Please remember- the Ohmmu LITHIUM not working is a SIDE EFFECT of Tesla making a much more reliable 12V LEAD ACID management system which has been proven over the last 18 months to be quite effective for the 99.99% of cars with the stock battery. It is not Tesla actively blocking the Ohmmu battery. It's just Tesla correctly detecting that this is a battery not acting like a healthy lead acid battery.
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