[RE-wrenches] Different LFP Batteries in Parallel

[Steve Higgins]

I wouldn't do it... By doing so, you'll likely void any manufacturer's
warranty.

If you must do it, I would manually balance the old/new banks every 60-90
days. This involves separating the parallel strings of batteries and
charging each string independently to achieve a full charge. If you don't
do this, the different ages can cause imbalances, which will lead to
problems with the BMS, regardless of whether it is in open-loop or
closed-loop configuration.



*Steve Higgins* *⋅* *Technical Services Manager*
*t* +1.902.597.4020   *m* +1.206.790.5840
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On Mon, Jul 14, 2025 at 4:09 AM Jason Szumlanski via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> There are never-ending videos on YouTube showing different brands and
> capacities of LFP batteries working in parallel. I have never tried it
> myself, and every instinct says don't do it, but I have a situation where
> it would be very helpful.
>
> I have a client with an older 60 kWh battery that is discontinued and
> incompatible with any other battery from the same manufacturer. It has a
> BMS with a 51.2 volt nominal rating. They need another 20 kWh of capacity.
> It is too costly to scrap the existing battery and start over, and the
> existing battery has been tested and confirmed to hold very close to its
> rated capacity.
>
> What is the real deal on mixing and matching? Is anyone doing this safely
> and successfully? I wonder what the battery manufacturers say about it.
>
> Jason Szumlanski
> Florida Solar Design Group
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