12v battery issue.

[VIK P]

After having original battery replaced 20mo. ago it was 6yrs. old. New replacement interstate battery. Was completely dead this morning. How can I load test? 

[homestead]

Take it to a battery place they will load test it for free.

[Givmedew]

There are too many people who own Fords that go 5+ years on the original battery and then 12-24m on the replacement.  

I’m convinced this is usually caused by not resetting the Battery Management System when the battery is replaced.  I would recommend doing this with FORScan yearly so you have confirmation that it was done.  But it can be done without FORScan however on the CMax there is no visual or audible confirmation. 
 

I’m convinced that not only is your battery management system configured to charge AGM not SLA like your new battery may be but I also believe that the primary issue with the BMS is that it monitors the amount of power that is used on the system.  Over time it is my understanding that Ford slowly reduces the amount of energy that it puts back into the battery.  Who asked them to do that?  Who told them it was wise to do that while also not paying more attention to the SoC based off of resting voltage?  I have no clue.  But I can tell you this… your battery was likely destroyed slowly over time as it slowly put less and less charge back in than was used and the case is even worse if your battery wasn’t completely charged before installing it.  Over time your resting battery voltage goes down below 12.5V which will start causing damage slowly to an SLA, an AGM might be able to handle the SoC associated with 12.5V but soon even an AGM is going to start taking damage.  At 12.4V resting an SLA is really starting to feel the pain at 12.11V long term (like months) it’s definitely cooked.  Anything below 11.8V and even very short term this is extremely bad for the battery.  While an AGM could potentially recover from that Voltage.

 

So if your new battery isn’t AGM and the BMS wasn’t reset you have 3 things going against it.:

-1) It can not take as deep of a depth of discharge as AGM it isn’t a deep cycle.  It’s generally accepted that anything further than 50% depth of discharge will greatly reduce the lifespan of a standard SLA.

-2) without reprogramming the vehicle to treat the battery like an SLA the car will treat it as an AGM.  Also capacity it programmed as well and SLA may have a higher capacity and that might actually make things worse of how Ford charges the battery (larger capacity have longer service lives on dumb cars). 

-3) it’s my understanding that without constantly resetting the BMS every few years that Ford will slowly start reducing the SoC voltage because it doesn’t not pay enough deference to the resting voltage of the battery and might not even consider it greatly.  If it’s only paying attention to adding back a certain amount of watt hours or amp hours after using them and it slowly reduces those then over time the resting voltage will keep dropping.  
-4) bonus reason… a 12V SLA has slightly different voltages for its SoCs while 100% on an AGM is higher than 100% on an SLA just about everything else is lower on an AGM.  So an AGM can safely sit at 12V all day with little to no advanced aging.  So the Ford BMS would find it perfectly acceptable to let the battery go to 12V.  On an SLA 12V is definitely bad for the battery.  On an AGM 11.7V is getting a bit low but it’s still doable but will start slowly ruining the battery.  On an SLA 11.7V is straight murder and at 11.6V an SLA could potentially take freeze damage at -7 to -10C even at a higher voltage of 11.7 it might take damage at -15C to -20C vs nearly impossible temperatures for a fully charged battery.  The damage voltage for AGM… much lower.  
 

To test resting voltage it’s best to disconnect the battery and let it sit for 30 minutes or more.  But alternatively you can connect a multimeter to the cars jump post under the hood and a ground then set the meter where it’s easy to turn on and read without touching the car.  Let the car sit for several hours then go back and without opening any doors or unlocking the car turn on the meter and check the voltage.  If you unlock the car the voltage will likely go up if the DC-DC activates.  I don’t know what the terms of activation are but on my i3 REx it was literally anything that wakes the car.  Also if you have an Energi don’t plug it in.