Large battery banks can have cumulative mismatch sums that exceed the balancing capability of most standard BMS units.
We utilize a 4 step process:
First, for raw cells, we charge your entire shipment of batteries in parallel up to 3.65v, and let them float until the current tapers down to <100ma for the whole pack, meaning that all of the cells are fully charged and top balanced. This can take quite some time, even with our industry leading test & measurement equipment. For pre-built packs, we charge with the main battery connections, however we do not top balance the pack. If possible, cell voltages will be recorded
Second, we capacity test at a .2c (C/5) rate, ending at 2.5v/cell. For this test, we will connect your batteries the same way you would have them connected in the kit you purchased, so the data matches your real-world application. We will run the test at constant current, loaded with an HP/Agilent 6050A electronic load, while measuring each series connected block utilizing an HP/Agilent 34970A data acquisition unit, which will log every cell’s voltage as well as the current draw on the pack. This data is logged in a CSV file which we will send for your records.
Third, after capacity testing, we will charge your pack 30% SOC for shipping.
Finally, each cell will labeled to identify which batteries need to be connected in parallel and series, in order to ensure that the top balance is maintained when installed.
This process is time constrained by the physical properties of the batteries and cannot be rushed; please allow extra time for delivery.
If you would like to see our testing apparatus, we made a video, available in the videos tab.
Sure wish I had just paid them to do it, did it myself and it cost me more money and a headache.