[RE-wrenches] replace part of rolls battery bank

[William Miller]

Daniel:



I feel your pain:  In October of 2021 one of our off-grid clients had
failed flooded L-16 batteries.  We needed 16 replacement batteries and
chose Rolls VRLA batteries.  We could not get 16 due to supply chain
constraints so we went for 8 with a back order for another 8.  It took
until May of 2022 before we could get 8 more.



The Rolls batteries subsequently failed.  We were denied warranty relief in
part because we mixed the exact same batteries but delivered 7 months
apart.  The cost of resolution came out of my pocket.



If you can’t mix the same batteries of slightly different age, I would
extrapolate that you can’t mix batteries of different manufacturer.  My
guess is if you mix batteries the entire array would experience a hastened
decline.  This conclusion is consistent with research done over many years.



I looked up the S550 batteries and learned they are 6 volts units.
Assuming the system is 48 volt nominal this would be 3 strings of 8.  Three
strings is pushing the envelope of acceptable design.  Multiple parallel
strings encourage circulating currents resulting in a process I call
“battery cannibalism”:  Lower voltage batteries discharge the higher
voltage batteries over time.



If it were me I would rearrange the batteries into two strings of the best
batteries and wait for the rest of them to fail.  I would then redesign the
system for one string with an appropriate AH rating.  Two volt cells are a
practical way to achieve this.



Also look carefully at your thermal compliance.  Make sure you are using
the proper temperature compensation value applied to all charging sources.
Avoid re-radiated heat from sunlit surfaces and proved good ventilation.



I hope this helps.



William Miller



Miller Solar

17395 Oak Road, Atascadero, CA 93422

805-438-5600

www.millersolar.com

CA Lic. 773985





*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
Behalf Of *Daniel Young via RE-wrenches
*Sent:* Monday, April 3, 2023 11:04 AM
*To:* RE-wrenches
*Cc:* Daniel Young
*Subject:* [RE-wrenches] replace part of rolls battery bank



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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