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Discussion Starter · #1 ·
2018 Focus ST (North America): I recently changed from a leaky, weak OEM battery to an Odyssey Performance AGM96R. I reset the BMS without issue using FORScan, and then started looking at other options in the BCM programming. There are a couple of entries there related to the battery: one for Battery Type/Size and another describing Capacity. They both seem to have similar entries. Neither entry has options for this exact battery, and the one option that shows AGM has very different amp hours and CCA than the replacement.

Should I just try to match up the amp hours, or is it important for some reason that I tell the BCM that the new battery is an AGM? Do these two entries need to match? Does anybody know how the BCM actually uses them?

Does anybody know how the BMS works on our cars?

Thanks,
G
 

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2018 Focus ST (North America): I recently changed from a leaky, weak OEM battery to an Odyssey Performance AGM96R. I reset the BMS without issue using FORScan, and then started looking at other options in the BCM programming. There are a couple of entries there related to the battery: one for Battery Type/Size and another describing Capacity. They both seem to have similar entries. Neither entry has options for this exact battery, and the one option that shows AGM has very different amp hours and CCA than the replacement.

Should I just try to match up the amp hours, or is it important for some reason that I tell the BCM that the new battery is an AGM? Do these two entries need to match? Does anybody know how the BCM actually uses them?

Does anybody know how the BMS works on our cars?

Thanks,
G
I am curious about this as well............. :unsure:
 

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I haven't looked through Forscan yet for this but can you set the parameters individually (ie CCA, Ah, battery type)? The charging profile for AGM and standard batteries are different and not setting it correctly will lead to premature failure, especially with a deep cycle battery.
You will have to do a Batt Life Monitor reset as well. It's floating around the site here somewhere.
 

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You will have to do a Batt Life Monitor reset as well. It's floating around the site here somewhere
 

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Discussion Starter · #5 ·
I've already reset the BMS with FORScan. I'm assuming that's what you mean by Battery Life Monitor reset.

I did some more reading today and also talked to a guy in a local ST/RS club who coincidentally works in a battery factory.

AGM batteries (like all batteries) have a maximum voltage differential between charge voltage and battery voltage, above which they will get over-excited and vent water vapor and/or oxygen and hydrogen gas. The upper threshold varies depending on who made the battery. For traditional FLA batteries it doesn't matter as much because you can add water back. But for AGM, since they are sealed, the loss is permanent.

For the Odyssey 96R which I installed, the manual states an ideal charge voltage range of 14.1 to 14.8 volts and to not exceed 15v. This is in reference to putting the battery on a charger.

I'm not sure what our alternators will put out, relative to instructions from the BMS. I get the impression from reading that short-term excursions above 15v would be OK, or at least tolerable in terms of overall impact to battery life. But you don't want it to be sitting above that 15v for long periods of time. This is what -CAN- happen if you don't reset the BMS.

Anecdotally, the thing will reset itself after the car is off some period of time. And, also anecdotally, it is constantly self-calibrating on some schedule.

The other thing the manual mentions is that to maximize battery life (again, for this specific battery) you want to keep the thing charged to 12.85 volts as much as you can.

Anyway to answer the original question: do I need to change anything in the BCM programming? In my case probably not. The Odyssey 96R pretty much matches OEM specs as to CCA and Ah and reserve capacity. The values currently reported by FORScan correspond to the OEM battery. So I'm going to leave mine alone, for now anyway. I will keep an eye on my battery voltage for a while and see what happens. When I looked earlier, it was 12.65 volts, which the manual states is about 80% charged. As mentioned, 12.85 is considered 100% for this battery. If you let batteries drain to low voltage for long periods of time, it will impact battery life. AGM is reportedly much better at tolerating this than FLA, but it still doesn't like it. For my battery, according to the manual, less than 12 volts is the threshold where permanent damage can occur.

12.65 seems kind of low, especially as I went on an hour-long drive after installing the battery yesterday, but I am also waiting on a replacement positive battery terminal. The original one had corroded so badly it is probably 50% gone after cleaning all the blue crap off of it. Amazingly, the negative terminal appears nearly pristine. I guess I'm glad the Ford dealer lost my battery cover.

If the voltage drops any further below 12.65, I will probably experiment with other values in FORScan to see if I can get it to start climbing.

I realize also there may be some phantom load somewhere in the car, but I don't really know how to check for that, or identifying that there is one present, how to figure out what it is. If I have to throw this thing on a tender, so be it, but what a PITA.
 

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You're just awesome. I will consume a 7yo Havana Club Anejo and Coke in your honour!
@Jurld Sounds like you've done your research and thank you for sharing. I found this on the Forscan forum and a little more digging there might be beneficial. Changing battery type? - FORScan forum
As you mentioned the biggest concern is not consistently floating the battery over 14.4V for longish lengths of time. This is also the case on the deep cycle batteries I used to maintain on solar setups.
 

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Discussion Starter · #8 · (Edited)
OK, so more information. I found "test" mode in the car (hold down the "OK" button on the left side steering wheel controls when you turn it on until the LCD in the instrument panel indicates Test) and cycle up a few screens to show the battery voltage.

Sitting without the motor running this shows 12v. Which is below the threshold where Odyssey says risks permanently damaging the battery.
Sitting with the motor running, or driving around, this voltage fluctuates quite a bit, but seems to mostly be around 12.2v or, if I turn on the lights, 13.4v. The range of values seem far below what I'd expect (13.6 to 14.5 volts when the motor is turning the alternator)

I don't know if this voltage reported in test mode is accurate.

Putting a meter on the battery after I parked it the last time showed the battery held about 12.5v, which is not fully charged, per the manual, but also not in the danger zone (below 12v). At some point today I am going to do some more tests with the meter with the motor running to see what I can figure out.

My meter is very old and I don't know how accurate it is. Tenths of volts are important here.

I have in hand a new positive cable (the original was corroded very badly) so I will be curious about if anything changes when I install it. The positive supply to the battery manager appeared intact, but maybe its integrity is compromised more than I can see.
 

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Discussion Starter · #9 ·
Installed the new positive cable. The battery had fallen to 12.3 volts since the last time I tested it with the multimeter. Cranked the engine and battery was reading 14.3v. Went for a drive for an hour or so. Before shutting off the motor, battery was at 12.65v. This all seems normal to me.

I forgot to put it into test mode, so I have no idea what the instrument display would have been showing.

FWIW, I cut into the old cable and the positive lead to the BMS was pretty badly corroded inside the insulation/tape.

I'll probably check it with my meter over the next week or so. I'm still wondering about it dropping .2v in 48 hours just sitting in the garage.
 

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I'll probably check it with my meter over the next week or so. I'm still wondering about it dropping .2v in 48 hours just sitting in the garage.
New cars with all their electronics always have some paristic draw; this does not surprise me since the battery was a bit down on power from the bad cable
 
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Discussion Starter · #11 ·
Battery dropped another .2v overnight. Went out and did some errands this morning, made a few stops. Checked it while the car was running and battery is down to 12.1v. This is not making me feel warm and fuzzy. . .
 

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Discussion Starter · #12 ·
After work I finally spent enough time with FORScan to learn how to set it up to read telemetry from the car. Among other things, it will tell you:

  • battery voltage
  • battery current in/out
  • battery state of charge
  • voltage demanded
  • battery days in service

Things I learned:

The voltage reported matches what my multi-meter is reading.

Battery voltage had climbed to 12.3 volts since when I checked it earlier today at the end of my errands. How? Maybe temperature related?

The car reports voltage from 4 different modules, one of which is the APIM. The other three were very close to one another but the APIM voltages were a lot lower. I'm assuming that this is the value that shows up on the display in Test Mode since that is kind of what I remember seeing before.

The car thinks 12.3 volts is 70% charged. Maybe true of the OE battery but not of the Odyssey AGM I installed. This is one thing I need to change, if possible.

After starting the car, it was asking for and getting anywhere from 14.8 and slowly dropping towards 13.1 volts as it recharged the battery. State of charge returned to 77% pretty quickly and then it took it a while to hit 78% and then finally 79%. This was over a 10 or 15 minute drive with the AC blowing and the radio on. I'm assuming that it must have some target SOC that is not 100%, presumably 80%. So that's another thing that I need to change, if possible.

I feel I need more data and that probably involves taking more of an extended journey like I did earlier today.

One hypothesis I have is that the system gets the battery to some target SOC and then lets it fall to some lower threshold before deciding to charge it again. I suppose for an AGM battery like mine this would be OK. The Odyssey manual states 12v is the bottom limit where the battery needs to be charged to avoid damage.

I also need to do more research about BCM programming and try to discover if it is possible to adjust these targets.

I'm also -really- curious about what would happen if you unplugged the BMS sensor at the negative terminal.
 

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Discussion Starter · #13 ·
I did some more reading and talking to folks who understand how this stuff works.. Based on the theory of operation, the BMS will generally attempt to get the car to 80% SOC and keep it there. Once it gets to 80% it will start doing nifty things like letting the alternator spin freely under acceleration and regenerate electricity under deceleration. The situation where my battery wound up being at less than 80% at the end of my trip was one where I made several stops and starts and did not spend much time in between, allowing the battery to recharge before arriving back at home. I also took the final measurement sitting at idle. It was a hot day, which also makes a difference.

Another thing I learned is that at some non-specified "long" interval, the BMS will cause the alternator to refresh the battery to 100% by charging it at "up to" 15.2v which is too much for the Odyssey AGM battery. The only information I've seen for "how long is the interval?" is from a manual for a newish Ford Transit that said it would do it if the vehicle sat for 30 days. I'm skeptical this is relevant to a Focus, but who knows. I know for sure I don't want to throw too much voltage at an AGM.

My plan of action at this point is to purchase a battery charger in order to top the car off periodically. I'd assumed that the alternator would charge the battery to 100% and clearly this is not the case. A charger will allow me to condition/refresh the battery at the proper voltage in order to avoid any potential for the car to try and do the refresh at too high of a voltage. I'm also wondering if, after I charge it fully and then let the BMS relearn the SOC, it will then treat 12.85v as 100% and thus avoid potential under-voltage issues.

I found some references on another forum that identified settings in the BCM that tell the BMS what % SOC to target. It's the only reference I've seen and it was from a while back. Nobody on that thread mentioned testing the settings. I did NOT see these in the BCM settings for the 2018 Focus in FORScan when I looked.
 
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