got some young 2012 modules

My experience has been that the charging Ahr is an unreliable number as these modules can be 'overcharged'. The excess charge is converted to heat and gas and results in lower discharge values on subsequent charge/discharge cycles. So my module tags have number pairs:

• charge - only IF the dV/dt trigger event occurs, usually just the first one. After the first or second charge, they typically stop only when the charge limit is reached.
• discharge - the usable capacity as this is what the battery module dumped.

To minimize damage because over charging leads to a loss of subsequent discharge capacity, I put a charge limit. This is typically is typically no more than 5.5Ahr. After the second discharge becomes the value I use for a module. With the MRC 989, a cycle consists of:

1. initial discharge to the lower limit voltage - typically 6V for these module or 1V per cell. Since we don't know the initial state, this number is not useful
2. initial charge to the dV/dt or charge limit, typically 5.5Ahr - if the module reaches the charge limit, it is usually not a good sign. It means the dV/dt failed to stop the charge. Because I get no indication of what stopped the charge, I record but don't really worry about this value until I have several others. Exceeding 8V per module is overcharging the modules that reduces capacity.
3. first full discharge to 6V per module - this is the initial Ahr capacity and typically the maximum that will be seen.
4. second full charge to dV/dt or charge limit - if the charge stops before the charge limit, we know the dV/dt logic worked. This is always higher or equal to the first full discharge but not usable for module Ahr capacity. It is only discharge capacity that has any use . . . but then the module has no charge and can not be used for anything else.
5. subsequent discharge/charge cycles - interesting to establish a pattern but always I find lower discharge capacity than the first. I see no evidence that cycling these modules increases capacity.

So when I see a report of charging to '8.4V', well I'm glad these are not my modules. One of the reasons for using a low charging current is these modules are somewhat tolerant of low, current, overcharging. The literature points out and a temperature probe confirms the temperature rises, swelling shows the internal pressure grows, as the internal chemistry converts H{2} and O{2} back into H{2}O and a bunch of heat. In overcharge, the module is just an expensive resistor.

Bob Wilson

 

These modules are fairly tolerant of some over-charge especially at low amps . . . unlike some LiON batteries. But no battery likes it. This really is a case where ~8.0V should be considered, in my opinion, the maximum. I have seen as high as 8.8V using my MRC 989 BUT there was no charge happening. The modules were just getting warmer and warmer.

They are still good and given your discharge only went to 7.0V and you saw 1.6 Ahr, I'm expecting you'll find about 3.5 Ahr capacity. There is a heck of a lot of charge remaining between 7.0V and 6.0V.

Bob Wilson

 

My experience has been that once the first, full discharge occurs, the module stays at the same or slightly lower, discharge capacity regardless of how many times it is cycled. I've only found one way to get the full capacity back but that is extremely experimental.

After you swap the modules and have the car running with the new modules, I'll talk and show you how this experimental approach works. Understand, EXPERIMENTAL, which means the reworked modules may be considered junk afterwards. That is why we only want to do it with 'scrap' modules.

Bob Wilson

 

I've not seen used modules having more than 5.1-5.2 Ahr capacity but I haven't been dealing with the newer style modules.

I have one sample of the new style plus the 38 in my rebuilt pack . . . in service. Still, I probably would have started less than the 6.5 Ahr capacity of a new module. Still, you're at the leading edge.

Bob Wilson

 

You only measured the charge cycle on 38. Run the discharge cycle and I'll bet you get a satisfactory number.

 

I have followed this whole thread and it is my belief that every module you have is not only good or acceptable but, very good.