[RE-wrenches] replace part of rolls battery bank

[Howie Michaelson]

Daniel,
If it was me, I wouldn't do it.  The biggest issue is that dissimilar
batteries (as well as different age batteries) have different internal
resistance.  This will only exacerbate the problem with running multiple
strings of batteries - that is they will charge and discharge at different
rates, causing the individual batteries to drift farther and farther
apart.  And even if the new batteries settled down into a similar
charge/discharge routine as the remaining bank, my experience has been that
often, when a couple batteries in a larger bank die, they are only the
first of many to find their way to becoming boat anchors. So you will
potentially find yourself needing replacement of more batteries sooner than
you'll be happy about.
My suggestion would be to sort through the remaining batteries to find the
healthiest 16 (through load and specific gravity testing), rearrange the
bank into 2 strings of 8, keeping the others for replacement of future
potential failures.  This will give you some breathing room to propare to
make the investment into a full replacement bank, be it Lead-Acid or
Lithium.
Howie

*Howie Michaelson**Sun Catcher*

*NABCEP Certified Solar PV Installer™*

*Solar Electric Systems Sales & Service802-272-0004*


On Mon, Apr 3, 2023 at 2:04 PM Daniel Young via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Hello Wrenches,
>
>
>
> Have a client with 24 x Rolls S550’s. 2 of the batteries have given up the
> ghost. Rolls will replace them under the pro rated warranty.
>
>
>
> The issue us, the client is wanting to replace them with non Rolls
> batteries to save $. They can get 400AH 6V L-16 form factor FLA batteries
> from a local battery house for the same price I am going to get the new
> Rolls for. And that also means they don’t need to pay for freight. The net
> result is that they could save $4-500 by getting the batteries locally. No
> freight, and no markup on the batteries we provide (I can technically add
> the lost markup back in as labor, we do need to make something off of the
> 3hr one way drive to swap the batteries)
>
>
>
> Question is, has anyone got experience mixing battery brands like this?
>
>
>
> 3 x strings of 8 c S550’s (L-16HC would be the replacements) both dead
> batteries are on the same string.
>
> Whole battery bank is near the 5yr old mark.
>
> The last rolls battery bank the client had lasted them 10 years. (they
> baby the battery bank to be sure, and take maintenance seriously)
>
>
>
> I understand where the client is coming from, but do not want to let them
> shoot themselves in the foot, and I simply do not know what the chances are
> of swapping in batteries from a different brand. In my head, I don’t see a
> big issue, even if they are sub par, they will likely just get older
> faster, and fail around the same time as the rest of the 4-5yr old battery
> bank. But I’m unsure if there are any more subtle issue that these other
> batteries would cause.
>
>
>
> Client has been loyal for more than a decade, so I want to give them a
> fair shake at saving some $ now, as they plan to move to lithium when the
> whole battery bank finally gives out.
>
>
>
> With Regards,
>
> --
>
>
>
> Danny Young
>
> NABCEP PV Installation Professional #031508-90
>
> Engineering Team Lead
> Solar Energy Solutions
>
> Lexington | Louisville | Bloomington | Cincinnati | Evansville |
> Indianapolis
>
> 513-448-5176 (mobile)
>
> 877-312-7456 (Main Office)
>
> danny at sesre.com
>
>
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