[RE-wrenches] Different LFP Batteries in Parallel

Mon Jul 14 08:55:36 PDT 2025

This client has been advised that it's not a good idea, and any failures might
result in a complete battery replacement. If he goes forward, it will be at his
own risk.

They have a full-time homewatch person who is quite capable. He could monitor
SOC and also isolate banks for balancing efforts if necessary. We have a nice
Midnite 2000A battery combiner there with breakers for each battery, so it would
be pretty convenient. 

Self-insured. I don't think any of my off-grid barrier island clients have
insurance. The mainland insurance market is messed up in Florida. Forget about
the islands.

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208

On Mon, Jul 14, 2025 at 11:31 AM Dave Angelini Offgrid Solar via RE-wrenches
<re-wrenches at lists.re-wrenches.org> wrote:

> Does the client know that they can't blame you for doing something that has
> chances of being a bad choice?
>  
> Can the client keep track of two different Soc and be responsible about it?
>  
> I would also look into how a home insurance policy would react to a claim.
> 
> 
>  
> 
> Dave Angelini Offgrid Solar
> "we go where powerlines don't"
>   http://members.sti.net/offgridsolar/https://offgridsolar1.com/https://offgridsolar1.com/ http://members.sti.net/offgridsolar/
> e-mail  offgridsolar at sti.netoffgridsolar@sti.net
> text 209 813 0060
> 
> 
> 
> 
> On 2025-07-14 6:45 am, Jason Szumlanski via RE-wrenches wrote:
> 
> > They are Lithionics. 
> >  
> > 
> > Jason Szumlanski
> > Principal Solar Designer | Florida Solar Design Group
> > NABCEP Certified Solar Professional (PVIP)
> > Florida State Certified Solar Contractor CVC56956
> > Florida Certified Electrical Contractor EC13013208
> > 
> > On Mon, Jul 14, 2025, 9:33 AM jay via RE-wrenches <re-wrenches at lists.re-
> > wrenches.org [re-wrenches at lists.re-wrenches.org]> wrote:
> > > Hi Jason,
> > >  
> > > can you let us know what the old battery is so we can dig up the specs and
> > > see if there would be any issues.  
> > >  
> > > There are a few odd ball like simpliphi which while a 51.2v has a very
> > > narrow window for operation compared to most other prismatic cells.
> > >  
> > > jay
> > >  
> > >  
> > >  
> > > 
> > > 
> > > 
> > > 
> > > > On Jul 14, 2025, at 5:07 AM, Jason Szumlanski via RE-wrenches
> > > > <re-wrenches at lists.re-wrenches.org [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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