Longer term Ohmmu experiences?

[Durzel]

Hi

Looking at possibly buying an Ohmmu lithium (LiFePO4) battery to replace the OEM one in my Model 3. The car is approx 18 months old and from what I can see from stats it has started waking up to top up the 12v battery every 24 hours, so I don’t think it’ll be too long before it says it needs to be replaced…

I tried reaching out to Sean @ Ohmmu to ask a few questions but got no response, which is a bit of a concern (e.g. for future warranty claims). I’m hoping some existing owners might be able to help.

I’ve got an automatic trunk and frunk kit fitted to the car. I’m led to believe both draw a nominal amount of power when idle, but it’s obviously enough that it is draining my 12v enough to need topping up. I should say that I barely drive my car, which possibly isn’t helping. I’ve done just over 2000 miles in those 18 months, and quite often won’t need to drive it for weeks at a time.

I’m keen on the Ohmmu on the basis that it should in theory last longer between topups, but at the same time I’m worried that the usual battery topup procedure doesn’t work with it? How does an Ohmmu fare in a lightly used car?

Also it gets pretty cold over here in the UK. Sub zero temperatures are common in winter, although they aren’t usually more than single digits. Bearing in mind the above is it possible that the car wouldn’t be able to recharge the battery if it’s too cold out, and therefore might go flat?

Thanks in advance for any help provided.

 

[jjrandorin]

There are a few different threads in the model 3 subforum on this battery. Perhaps one of the following couple threads has some information for you? I havent read them all but know there is quite a bit of discussion about this battery.

Ohmmu 12V Battery Feedback

i bought the Ohhmu battery for my Performance Model 3. It worked great until there was an update from Tesla. Apparently, Tesla is aware that this battery is not OEM and through the software quarantines it. Ohmmu tells me they are working on it, but no solution yet. I bought a Tesla battery...

teslamotorsclub.com

What's with the Ohmmu 12V battery?

I see a lot of strong recommendations for the Ohmmu 12V battery. It's a Lithium-based 12V replacement. Plenty of statements of this being a life-altering change to their vehicles, feeling lighter, etc. But I'm not getting it. $720 (Canadian) off Amazon can pay for a lot of typical lead-acid...

teslamotorsclub.com

See if those help.

 

[Durzel]

Thanks. Not sure how I missed the first one but it’s got some useful info.

 

[jjrandorin]

One more thing... because of the age of the threads, you might find a lot of discussion on version 1 of the battery having an issue with some firmware update or other. I dont have one of those batteries, but was following that discussion out of curiosity. In the end, it appeared that Ohmmu both worked around whatever the issue was with the firmware update, AND swapped out previous purchasers with the "version 2" version of the battery which corrected the issue.

I remember very clearly being impressed that a "small" company was able to take care of their customers like that.

 

[Durzel]

Yeah I was aware of the firmware that messed it up, and their response (which was good). It does tend to suggest that there might be an element of risk for future updates causing similar problems, due to Tesla changing monitoring parameters or whatever on a whim.

My main concern really was that because I don’t use my car much my usage is probably different to most people who have got an Ohmmu. It’s only because I don’t drive my car for weeks on end that I’ve even noticed and been able to track when it’s spontaneously waking up (and why). If an Ohmmu helps in terms of being able to stay charged (or have more capacity) for longer, then all the better for my needs.

 

[jjrandorin]

Yeah I was aware of the firmware that messed it up, and their response (which was good). It does tend to suggest that there might be an element of risk for future updates causing similar problems, due to Tesla changing monitoring parameters or whatever on a whim.

My main concern really was that because I don’t use my car much my usage is probably different to most people who have got an Ohmmu. It’s only because I don’t drive my car for weeks on end that I’ve even noticed and been able to track when it’s spontaneously waking up (and why). If an Ohmmu helps in terms of being able to stay charged (or have more capacity) for longer, then all the better for my needs.

Yeah, I totally hear you. I was considering one for myself, but "preCovid", I drove about 18k miles a year just driving to work and back. 2020, I drove 6k miles, and this year so far, even a bit less.

I decided against getting it simply because of cost. When I sat down and looked at it, the Ohmmu was > $400 and the OEM battery was $85. I came to the conclusion that I could simply buy a new OEM 12V battery pre emptively every 2 years, and the "break even" on the ohmmu was greater than 4 swaps, or 8 years... provided it had no issues during that time.

I came to the conclusion that one would have to go for the Ohmmu or MPP battery for something other than cost (which many do), because the relative lack of cost of the OEM tesla model 3 battery ment you could treat it as a disposable part. The part itself is $85, and installed by tesla mobile service in my driveway while I was working was $129 "out the door". Still roughly 4 changes before I broke even, and as much as I like this car, I will probably have a newer model 3 8 years from now.

 

[Durzel]

Thanks. That crystallises it for me too.

I have Tesla doing remote diagnostics on my car at the moment to determine the reason for the 24 hour wakeups, but I already know what it’s doing, and why, i.e. the two aftermarket kits I’ve got fitted.

Most people probably wouldn’t experience what I’m experiencing because they drive their cars every day or every other day, enough to charge the 12v on the go, but in my case it’s almost always just sat there, so any wakefulness is conspicuous and remarkable.

Anyway, I’m rambling now. Although my car is under warranty I’m expecting Tesla to say I have to pay for a new battery because of the mods (can’t really argue too hard on that one), hence considering the Ohmmu. I’ll have a look at the pricing here in the UK - I suspect it would be more than $85!

 

[a64pilot]

unless I’m mistaken, the dark current of those mods is really minimal
If you can get the OEM battery as cheap as we can in the US, you cant make a fiscal argument against one, but if OEM is expensive, there are other very good deep cycle group 51R batteries, notably Optima and Odyssey. US brands, I’m sure there is an European equal if they are stupid expensive over there.

From what I have read on here about the Tesla charging behavior, I have to think that maybe a lot of the problem is the OEM battery may not be the best quality.
I think there may be a middle ground between the Uber expensive LifePo4 batteries and the inexpensive OEM.

 

[rrolsbe]

My 2018 Model 3 has never slept for 24 hrs even after the PCS board and 12V battery were replaced last August under warranty. This assumes (like you) I do not charge or drive the car for several days. I thought the original battery was getting weak but the new battery still needs to be topped off after around 17 hours of sleeping and it takes about 2 hours to top off.

BTW, I use a bluetooth voltage monitor to record the 12V battery voltage levels which makes it real easy to see the sleep/awake status of the car. The monitor draws 1ma and records about 32 days worth of data.

 

[jjrandorin]

FWIW, My model 3 is a Dec 2018 model. After going through the mental gymnastics above, even though mine was "fine" according to tesla remote diagnostics, I just scheduled an appointment and paid for it to be replaced preemptively, as I mentioned. I am curious how much it is where you are, please share when you find out. Perhaps its £85?

 

[Durzel]

Thanks all.

I think maybe this time around I'll just see about getting another OEM battery as preventative measure, and maybe explore lithium or whatever (or not) in the future. As was remarked above the cost of one Ohmmu battery buys at least 2, maybe even 4 OEM replacements (I'm in the UK so shipping is $99 anyway, plus whatever customs duty/taxes I would have to pay).

For the curious, here are my stats:

You can see that when I have driven the car somewhere (the bigger blue bars, from the car staying online with Sentry on) the car has actually slept for longer afterwards before needing to wake up to charge the 12v, which would suggest that driving and/or the car being online for extended periods actually actually does more to maintain the 12v than the car just waking up to do it does.

Back in May of this year the car would be asleep for several days at a time before needing to wake up to charge the 12v, and that progressed to waking up every 48 hours to do it, and more recently every 24 hours. Tesla have already confirmed to me that the 2 hour wake periods are "the car supporting the low voltage battery".

I did think about getting a Bluetooth monitor for the 12v but to be honest all its going to tell me is what I already know, a very slow parasitic drain from the two automatic trunk/frunk kits I've got installed.

The other thing I'm considering doing is having some kind of switch inside the car to physically disconnect both these kits for extended periods. It would make it more annoying to use the car (i.e. neither the frunk or trunk would open if disconnected, I'd have to open the car and then reach in and flip the switch to energise them), but given my car doesn't move for weeks at a time it seems more logical than having two kits just in a standby state, drawing energy.

 

[android04]

My 2018 Model 3 has never slept for 24 hrs even after the PCS board and 12V battery were replaced last August under warranty. This assumes (like you) I do not charge or drive the car for several days. I thought the original battery was getting weak but the new battery still needs to be topped off after around 17 hours of sleeping and it takes about 2 hours to top off.

BTW, I use a bluetooth voltage monitor to record the 12V battery voltage levels which makes it real easy to see the sleep/awake status of the car. The monitor draws 1ma and records about 32 days worth of data.

I agree that just because the car wakes up more often to charge the 12V battery doesn't mean it's getting weaker or there's a drain on it that the car can't monitor. It probably just means that Tesla updated the behavior to check on the battery and top it off more often, maybe as part of helping it last longer. If Tesla allowed the 12V battery to drain lower before (by having the car sleep for longer periods of time) perhaps they would sometimes drain it low enough that that it would start affecting the lifecycle of the battery. Lead acid batteries are healthiest when fully charged and you should never let them sit at a partial charge.

I installed a shunt and monitor on my Model 3's 12v battery in the summer and have noticed that it never discharges more than 5% of the battery before the car tops it off again. I think it's just a change in the programming that Tesla made intentionally. But it could also be due to my 12v battery being 44 months and 71,000 miles old.

 

[frank2371001@g]

I should do more research before buying the Ohmmu. A few weeks after installed. Tesla issued a software update. Error messages showed up. I reach out to Sean and this is his reply...Not sure I will get my money back.'
From: Sean Scherer
Sent: Friday, February 11, 2022 11:57 AM
To: Frank Ma
Subject: Re: Problem with my order 13299



Hi Frank, what is your order date? We have stopped selling these since December due to an update that Tesla did which has lead to the exact issue you are referring to. We are working on a solution but if you ordered since beginning of December we are honoring return extension for that period of time. The solution we are working on is a hardware solution that will be provided for free to any existing owners of our Model 3/Y batteries (only effected platforms).

 

[Dave EV]

I have Tesla doing remote diagnostics on my car at the moment to determine the reason for the 24 hour wakeups, but I already know what it’s doing, and why, i.e. the two aftermarket kits I’ve got fitted.

I don't think 24-hour wakeups are abnormal...

It probably just means that Tesla updated the behavior to check on the battery and top it off more often, maybe as part of helping it last longer. If Tesla allowed the 12V battery to drain lower before (by having the car sleep for longer periods of time) perhaps they would sometimes drain it low enough that that it would start affecting the lifecycle of the battery. Lead acid batteries are healthiest when fully charged and you should never let them sit at a partial charge.

This - I recently had my 12V battery (2018 Model 3 LR RWD) replaced after the car started warning it needed replacing - after almost 4 years, I'm not too surprised that it did given the high vampire draw of the vehicle.

But both before and after the replacement the car wakes up every 24 hours. Now sometimes it will wake up for 15 minutes - sometimes it will wake up for an hour.

I do think that a lithium battery would be an ideal replacement battery since they don't need to sit around near full to get maximum life like lead-acids do - in fact it's the opposite.

Anecdotal story - had a Optima yellow-top last almost 10 years in a Prius before leaving the dome light on too many times killed it. The OEM battery only made it 4 years. Not sure what how the construction of the Tesla OEM AGM battery compares to the Optima yellow-top....

 

[FurryOne]

I should do more research before buying the Ohmmu. A few weeks after installed. Tesla issued a software update. Error messages showed up.

I installed their v2 battery in my M3 back in 10/20, and everything was fine until update 2021.44.30.13, after which I got the Low Battery message and my USB stopped working. I followed their instructions to do a hard reset and the error went away for a short while. Now software 2021.44.30.14 is downloaded and won't install until I do another hard reset. Since they claim that their fix is hardware based, it'll be interesting to see what that is. Their timeframe for the fix sounds like it's on a boat from China.

 

[FurryOne]

I do think that a lithium battery would be an ideal replacement battery since they don't need to sit around near full to get maximum life like lead-acids do - in fact it's the opposite.

What Tesla needs to do is allow the selection of battery type in the service section - AGM, Li-Ion, LFP, rather than jerking around the battery manufacturers to try and fake Tesla's software into working.

 

[Durzel]

I can’t conceive of any situation where Tesla is going to provide workarounds for third party hardware.

 

[FurryOne]

I can’t conceive of any situation where Tesla is going to provide workarounds for third party hardware.

Well, they do it for rims - if you change from 19" to 18" or 20" they have you select which one you have.

 

[Durzel]

That’s for their own rims though, to account for people swapping between different Tesla ones.

 

[Flybyglass]

What Tesla needs to do is allow the selection of battery type in the service section - AGM, Li-Ion, LFP, rather than jerking around the battery manufacturers to try and fake Tesla's software into working.

That is actually a good idea. The issue came about because a software engineer added a feature to do 12 volt battery over charging tests. The Ohmmu or other Lithium batteries have a built in BMC that reads the over charge test and takes the 12 volt off line for a short period and that generates the errors. I would make the suggestion to Musk directly on twitter.