bad batteries = bad e-torque units?

[RAMTEXAS]

can someone who is knowledgeable clarify on this theory?
do bad/low batteries lead to premature failure of the e-torque units?
if not then what are some safety precautions to take in order to increase the longevity of the e-torque units?

 

[mikeru82]

There are actually two main components to the etorque system, a belt driven motor/generator unit and a 48v battery module. As there is no traditional alternator, the 48v battery module is what charges the main 12v battery, so if your main battery isn’t being charged you could have a problem with the 48v module. I guess theoretically a bad 12v battery could cause issues with the 48v battery module if it’s constantly trying to charge it. You can test your 12v battery if you suspect it’s going bad. I don’t know of any way to test the 48v battery module though.

There really aren’t any precautions to take to make either the MGU or the 48v module last longer that I’ve read about.

 

[RAMTEXAS]

As there is no traditional alternator, the 48v battery module is what charges the main 12v battery, so if your main battery isn’t being charged you could have a problem with the 48v module. I guess theoretically a bad 12v battery could cause issues with the 48v battery module if it’s constantly trying to charge it.

hmm this makes sense for the most part

 

[boogielander]

the 12v battery will always go before the 48v. if the 48v goes, you should see a warning light on your dash telling you there's an error in the charging system.
usually when the 12v battery goes, or about to go, you will notice significantly lower voltage during high load driving (ie, at night with lights on, music bumping, heated seats/ steering wheel on, etc)
you will also notice weak starts or hesitation to start after parked for a long period.

do bad/ weak 12v battery lead to premature failure of 48v batteries? could be, possibly, maybe.
I was running with a weak 12v battery (OE unit) for a few months, but because I have 400w of solar on my roof (most of the time 200w only because the other 200w panel is diverted for my Ecoflow so I can have fridge running 24/7/365), the starter 12v was getting charged during the day. That masked the weak/ bad 12v battery symptoms until that battery was so bad that it wasn't holding any charge.
Then, 3 months later, the replacement 12v battery failed due to internal fault, and was sitting at 0.3V for a few days. I noticed at night time driving my voltage dropped down to like 12.8v or so, even when my DC-DC is pulling power (which the BMS should tell the truck that it needs charge due to draw), and after a few weeks the 12v died. I know e-torque sits at 12.8 during driving at times, but that is when the starter 12v is fully charged and the ET DC-DC stopped pushing power out and the generator disengages to prolong the system. But it shouldn't happen when my DC-DC is drawing.

Then, there's also me... with not one, but TWO external DC-DC charging systems on the truck, combined pulling about 40A when IGN is on. So the e-torque system is always working: two DC-DC systems drawing amperage from the 12V, which needs to be replenished from the 48v, which engages the generator to replenish the 48v. I'm 54k miles in, going on 4th year, and with the stress I put on my truck, I've only gone through 12v and not 48v yet (knocking on wood)

So, do bad/ weak 12v battery cause premature 48v system failure? At this point, it is still an unconfirmed theory - it CAN happen, since on paper that sounds logical as it puts more stress on the 48v system, but from my experiences of overworking my truck, it is still a theory and not confirmed.