Upsized battery

[METROMAN]

So I saw a YouTube video where a guy installed a 96R battery in his C-max, instead of the customary 67R one. The 96R has 600 cold cranking amps, while the 67R only has 390. I wonder if there might really be an issue with doing that , or if it would be ok. I'd want to do the battery monitor reset with the install if I was to do that. Anybody else installed one of those larger batteries? "Enquiring minds would like to know".

[plus 3 golfer]

Ford says that the replacement battery should be of similar size and battery age zeroed out.  Otherwise the algorithms may not work as intended.  What are they (those installing larger batteries) trying to accomplish?  The car will still work fine with a larger battery with no issues but load shed programs and charging will likely not give the intended results.  The C-Max battery is made by Interstate, has plenty of Ah capacity and will start the car at 10.1 V (verified by me) and likely a lower voltage.  By definition, 10.5 V represents 0% SOC.  CCR is not relevant.

 

From what I have observed / inferred by monitoring SOC and charging curves (Amps vs SOC) and the SM, replacing the BXT67R battery with a higher rated Ah battery (not the same as CCR), will more than likely result in the actual Ah capacity of the larger battery to be charged to the same Ah level as the BXT67R over time.  This is because the software assumes the installed battery is rated at 43Ah when new.  In order to charge a larger battery beyond 43Ah, one would likely have to put the battery on a charger overnight.  There is also a self discharge of lead acid batteries of about 5% a month.  Thus, the larger battery looses more Ah of capacity due to self discharge than the 43 Ah.  It is thus logical to assume that the charging algorithm will over time put the same amount of charge back to both batteries (Ahs) but the SOC of the larger battery will decline.  Lead acid batteries like to be at a high SOC.  The less the time the car is in ready to drive mode and the less the frequency of driving the car, the faster the SOC of the larger battery will likely fall.  This could take months to years depending on the Ah difference between the batteries.
 

When I have time I will post several actual charging curves from my recording of data.  The following are several important points I have validated / inferred from the data.

 

1) The SOC is determined assuming 100% SOC = 43 Ah of rated battery capacity when new.  It is hard coded and I have validated the 43 Ah.

2) The PCM determines the set point voltage for the DCDC converter based on difference between current actual SOC and the computed current maximum capacity (SOC max) of battery. This is why it is important to do a battery age reset when a new battery is installed.  The greater the difference between computed max SOC and actual SOC is, the greater the added Ah of capacity (added SOC) for a given period of time due to charging will be.  If battery age is not reset, the algorithm will continue to use the computed max SOC of the old battery and thus undercharge the new battery.  I have validated this.

 

3) The computed current maximum capacity of battery is based on “coulomb counting”.   The current flow into / out of the battery is monitored and via integrating the current flow, the Ah of capacity losses can be estimated as the battery ages over time. So, the computed max SOC is 100% less the capacity losses. The charge / discharge data is stored in four PIDs - cumulative discharge in sleep mode, cumulative charge when car is charging (for non-hybrid when ICE is on), cumulative discharge when car is in Accessory mode (for non-hybrid when ignition is on),  and the fourth is not used in hybrids (cumulative discharge when ICE is off). When the battery age PID is reset to zero, these charge / discharge PIDs are also zeroed out.  I have validated that coulomb counting changes the SOC.

 

Edited February 22, 2021 by plus 3 golfer

[METROMAN]

P3G, thanks for the quick reply. I ordered the MX+ obd reader yesterday, and will be downloading the Forscan software after the reader arrives. I'm interested to see what it says. 

[plus 3 golfer]

Great.?

 

Maybe you can help decipher what the units are in the 4 charge / discharge PIDs I mentioned above.  The problem is I never had a new battery, FORSScan, and the age reset done, at the same time except for last month when my battery was replaced.  Thus, previously the PID data was not synced to a new battery.  But, now with a new battery installed last month and the PIDs zeroed out, I hopefully over time will be able to watch the PIDs change value and link it to a change in maximum actual SOC by every so often charge battery full with charger.