15/06/2026
Why aren’t most batteries properly balanced when you buy them?...
This follows on from a recent post about balancing, and prior to that about the correct charge voltage of 14.2v. All these things tie in together.
When you buy a battery, be it locally made or international, it most likely needs a bit of balancing on its first charge. This can take some time and may vary from minutes to days depending on how out of balance it is, and what type of balancing system it uses. For some batteries, there may not even be a balancer installed or it can be incorrected set up.
There are 3 main causes of imbalance when new.
a) Cells naturally self-discharging at different rates during storage,
b) The battery hasn’t been balanced after assembly,
c) Balancer settings are incorrect (usually balancing at too low voltage).
Balancing happens automatically for our batteries every time you fully charge, so it's good practice to fully charge regularly to maintain good balance. This also ensures the BMS provides more accurate readings too.
So let’s go back to the start of the process…
For the majority of major battery manufacturers producing batteries for this market, cells arrive from the manufacturer and are put on a test bench individually. They fully charge them, then fully discharge them, then they will recharge them to about 40% SOC (i.e. they will put 40Ah back into a 100Ah cell). During this process they will measure various parameters, most commonly Capacity and Internal Resistance. These parameters are used to match the cells together as closely as possible for the pack size. Pack size can be just 4 cells for a 4S 12v battery, or could be 64 cells for a 4P 16S 48v battery. This is a good start to building a good battery and this is done almost universally for both perfect cells and B-grade cells.
Where this process falls a little short, is that there can be a range of capacities grouped together. So (an extreme example) if you put 40Ah into a flat 100Ah cell, it’s right on 40%. However 40Ah into a 104Ah cell leaves it down at about 36%. When these are used in a battery and charged, the 100Ah cell will fully charge while the remaining 104Ah cells could all still need another 4Ah to fully charge. If the balancer is capable of 2A, and runs 50% of the time (which is common), then it could take 4 hours to bring that 104Ah cell up to full charge. If there are 3 cells that are 104Ah, then it could take 12 hours. In reality this difference is extremely rare, and most batteries will balance in just a couple of hours.
Some manufacturers (e.g. PowerPaul) take the time to ensure this balancing process is done prior to sending the battery out. So a battery that’s delivered to you should balance out the self-discharge discrepancy very quickly, and in most cases won’t even be noticed that it’s happening.
We have seen a few examples (not ours) of batteries that had poor connections between cells. In those cases we witnessed odd balancing behaviour during charging and discharging, which actually unbalanced the battery significantly, before re-balancing providing the charger is set up to allow that. We have also seen examples of balancers not being enabled, or set up to run at the wrong stages or voltages. All of these can cause slow or worse, no balancer operation.
