Expanded Battery?

[mrpossoms]

Hey all!

So I've been poking around with my 2016 e-Golf for a bit, and recently I was scrolling through readouts from VCDS I noticed an interesting value under the HV battery's controller.

MAS07792 Expanded battery limits not active

This eludes to the possibility of expanding the traction battery in a supported manner. Does anyone here know anything about that?

Cheers!

 

[f1geek]

This has been discussed before here. I believe it may be a way for the BMS to access more protected capacity so that VW does not need to perform pack capacity degradation warranty work. Probably not what any of us want to hear, but as of now it makes sense. Thoughts, anyone else?

 

[mrpossoms]

Hmm... That's interesting... And actually I can also confirm from VCDS that the cells in the pack on not fully charged when the car says it is. Most were floating around ~4.0v where "fully charged" for a lithium-ion cell would be 4.2v. I always assumed VW was doing this to prevent pack degradation from the car sitting around with a full charge and not being used, but perhaps what you're suggesting is the case?

 

[f1geek]

Like most car manufacturers (except for Tesla), 100% on the dashboard does not mean 4.2 V at the cell level. Allowing 4.2 V cell voltage means the cathode is mostly empty of lithium (stressful) and the anode is full of lithium (stressful) so it is best to avoid this voltage for cell longevity. Much research has proven this to be true.
As far as the e-Golf pack goes, I have measured the 100% SoC at 4.10 V and am guessing the 0% SoC is 3.27 V (I have never let the pack get this low, so it is a guess). My guess is only 89% of the gross energy content, when new, is available. It is probably safer for VW to reduce the top buffer size, if necessary, to get more usable energy from the pack, if necessary, to maintain usable capacity above a certain threshold, but at the expense of faster degradation.The top and bottom safety buffer is for longevity, but over time and with use, degradation is inevitable, especially since VW did not provide an active thermal management system for the pack.