Charging Battery Modules – Part 1

To try and get familiar with the process, I attached the battery charger to the loose modules I purchased. *This is not a good idea* – the modules can apparently expand while charging and discharging. If this were to happen to any significant degree, I imagine the modules would be unusable. As it stands, I didn’t run into any problems, but the internet tells me it’s a thing that’s possible.


Things to figure out:

  • Charge rate
  • Charge cut-off capacity
  • Discharge rate
  • Discharge cut-off voltage
  • Number of cycles

To cut to the chase, this is what I settled on:

  • Somewhere around ~ 1 C charge rate, went with 5 amps
  • 7250 mAh charge
  • Somewhere around 0.1 C discharge rate, went with 0.7 amps
  • Discharge cutoff of 6V
  • 3 discharge/charge cycles

This is mostly in line with, but a little different, than the main content in the PriusChat forum thread I was as using as guidance. In effect, this discharges a module at 0.7 amps until the voltage hits 6.0V. The charger cools down for a few minutes, then charges up 7250 mAh (or until it hits the , cools down for a few minutes, then repeats 2 more times. If you’d like to be mired in details and endlessly search for the “most correct” answer, this is a great spot to spin off a side project.

As a layman, this appears to be contentious amongst laymen with professionals derisively telling everyone they can’t possibly expect anything to work without equipment costing a few orders of magnitude more and a degree or two to use it properly. I found this to be a bit frustrating to research, as it seemed untenable to DIY and on a tight budget. The success of this project and others who have done the same stands as proof that sometimes the best solution is the one that’s completed. I welcome more guidance here though, I’d appreciateĀ a concise “here’s the best way to do it”.

This whole process takes roughly a day and a half per cell +/- a few hours depending on the capacity of each module and it’s starting voltage. This is why the number of chargers is important – this isn’t going to go well if you only have one or two. With 8, depending how attentive you are, it takes a bit under a week. If you only had one (28 modules * 1.5 days/module = 42 days) I don’t think the process would go smoothly.

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