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Is trickle charging the 12v battery necessary?

Bubbatech

Member
Nov 2, 2019
101
169
Alabama
50% is better for battery degradation

90% is better for brick balancing and BMS calibration
The latter is clearly documented.

The former is not clear in terms of the magnitude of the difference. No one has compared the real world difference between holding the battery pack at 90 and 50% over a 5-10 year time scale. I strongly suspect the difference is smaller than most people think. Elon has said this, but Tesla has provided no data.

also, if brick balance gets bad enough, the entire pack becomes unusable and must be replaced.
 
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jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
20,193
25,797
Texas
The latter is clearly documented.

The former is not clear in terms of the magnitude of the difference. No one has compared the real world difference between holding the battery pack at 90 and 50% over a 5-10 year time scale. I strongly suspect the difference is smaller than most people think. Elon has said this, but Tesla has provided no data.

also, if brick balance gets bad enough, the entire pack becomes unusable and must be replaced.
Note that originally the Tesla Model S had three settings 50%(storage), 92%(daily), and 100% (trip) So those are documented by what they actually did. The slider came in only because the EPA changed the rules. If Tesla would have left it that way, the battery rating would have been an average. (Presumably this was done at the urging of the other automakers and fossil fuel companies).

The comment about battery balance needs citations, because the BMS takes care of the balance when plugged in. Charging to 90% (or 100%) helps the balancing algorithm create a correct value. As far as I know, the worst thing that happens with an out of balance battery is that the battery's capacity becomes artificially low until steps are taken to restore the battery. If the battery balancing circuits fail, then the battery would need to be replaced, but the cause in that case is the failed circuits, not the balance which is just an effect.
 
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smatthew

Active Member
Jun 9, 2018
1,297
2,248
CA Bay Area
I doubt that a pack could get so out of balance that it would need to be replaced. BUT, a severely out of balance pack could take a long time to balance. The pack is only capable of correcting 1mv of imbalance per 24 hours.

Jerry33 - on a model 3 the BMS only takes care of balance if the car is idle, AND the battery is >85% full.
 

hcdavis3

HCD3
Supporting Member
Mar 3, 2019
2,383
1,579
02571
I doubt that a pack could get so out of balance that it would need to be replaced. BUT, a severely out of balance pack could take a long time to balance. The pack is only capable of correcting 1mv of imbalance per 24 hours.

Jerry33 - on a model 3 the BMS only takes care of balance if the car is idle, AND the battery is >85% full.
I charge to 90% every day. Works great for me.
 

electrongeek

Metrology Fanboy
Nov 1, 2019
69
74
Maine
Waste of money and battery. Drive the car, enjoy the car. Plug it in when you’re not. It’s that simple.

Some people, with inquiring minds, like to understand how things function at a level of detail that most others don't. For them, this is something of a pleasure, and not a waste of money. Some people spend their free time watching cat videos on Youtube. Others are too busy working to worry about the car. YMMV.
 
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