How to charge a 4 cell module out of the car

[JoeS]

You have the solution! According to this NOCO Genius 3500 User Guide, the "12v Repair Mode" has a fixed 16.5v 1.5A output. That is 4.125 volts per cell. So, you're in business and can ignore the workaround discussion above.

You'll still have to watch it and unplug to ensure you don't overshoot your target voltage.

Please do make sure that your DVM is properly calibrated. The cheap (even free) Harbor Freight DVMs are useful, but some I've tested have been off by as much as 0.25v when reading 12v.

BTW, how are you getting the battery to the car? You might check the regs.

Edit: The name that NOCO Genius 3500 assigned to that mode is interesting as Repair Mode seems have been designed not only for attempting to jolt lead-acid batteries back to life, but also for 4S Lithium Polymer or Lihium Ion (https://www.differencebetween.com/difference-between-lithium-ion-and-lithium-polymer/). I guess they wanted to make sure that someone would not confuse names and inadvertently use it for LiFePO4 batteries, which would be disastrous, so there is no use of the word "Lithium" in that Repair Mode's description.

[vh2q]

Great! Thanks.

I can put it on a boat or there is an air charter service that says it's AOK to bring on board with me.

Will charge that sucker up to 4V per cell, and when I get to Bahamas, will charge the rest of it up (or discharge) to match (have hobdrive).

Anyone who wants a free vacation and is willing to pay their way to Abaco, is welcome to join me wrenching on this car. Food, beer and accommo is on me. Great bonefishing and offshore as well (charter, i don't have a boat). I think it will be late Oct before they open customs to visitors though.

[JoeS]

When charging the 4S module, be careful: when charging this module, be sure to monitor each of the four cells to ensure that they are tracking; i.e., that the voltages of each of the four cells are identical as the overall module voltage goes up.

How do I know this might be a problem? Earlier today I was slowly charging an old 11P16S LiFePO4 module with built-in BMS. After half-a-day of slow charging at one amp with amazing identicity of all sixteen voltages, I increased the current up to four amps to speed things up (still well under the 110A max spec) and it suddenly started to run away on me as the voltages on a few of the cell groups suddenly and dramatically increased. Luckily I was checking this every few minutes and shut it down before any damage was done (I hope). I need to go back and review the specifications as I'm shocked that the BMS didn't compensate.
Moral of the story: monitor the individual cell voltages carefully as you're charging your module.

[vh2q]

Hooked up NOCO in "repair mode" and it's bring up the 4 pack slowly. Took all morning to get from 4.06V to 4.15V. It's delivering 1.5A. So I think that's the ticket. I'll bring it up to 16V, check the balance, and then ship it over to the island. I'll bring the existing pack to 4V per cell and then swap out the bad module. It's a pretty piss poor design when ONE cell can bring the entire pack to its knees.

[coulomb]

Took all morning to get from 4.06V to 4.15V. It's delivering 1.5A. So I think that's the ticket. I'll bring it up to 16V...

Are you switching between volts per cell and total volts? Because if the 4-cell module total was at 4.06 V, then you have at least 3 ruined cells. My guess is three cells at 0V, and they aren't likely to come up in voltage. Even if they did, they're likely ruined, with very little capacity. As already mentioned, watch the individual cell voltages closely, or you could have a fire, even charging at 1.5 A.

It's a pretty piss poor design when ONE cell can bring the entire pack to its knees.

All EV batteries will be like this. It's an unfortunate situation, but failure like this is very rare.

[vh2q]

Pack seem to be OK, never went below 3.3V per cell, all cells coming up and equalized even though I am gang charging.

Going to swap this pack out soon. Meanwhile the car has stopped taking a charge at all .. lights on charger cord don't come on at all neither do fans. I am assuming voltage of the bad pack fell below min. Car sat for a year during covid mess.