Sol-Ark and EG4: pairing batteries and inverters across two brands

EG4 prints Sol-Ark on its batteries' compatibility lists. Sol-Ark does not print EG4 on its own. That asymmetry decides most of what follows: who supports the pairing, which warranty clause applies, and whether a UL 9540 system listing exists for the inspector.

This guide sets the two makers' documents side by side for these pairings: an EG4 PowerPro WallMount (EG4 now calls it the WallMount 280Ah All Weather) or a LifePower4 rack battery on a Sol-Ark 15K-2P, 12K-2P or 5K-1P, and EG4's own 18kPV and FlexBOSS21 inverters with batteries. Every figure is a manufacturer statement with its document and the date we read it. We have not tested any of these products, and a document saying a protocol exists is not the same as a maker saying the pair is supported. The general retrofit question is covered in will a home battery work with my inverter.

What each maker's list says

All read October 19, 2026.

Sol-Ark's guide is explicit about what absence means. A battery not listed "has not been certified to work with Sol-Ark hybrid inverters, or tested by Sol-Ark," though Sol-Ark adds that its inverters "can generally function with most 48V batteries." It also states that it "does not offer technical support for battery communications with battery models not listed in this Guide." The guide covers the 18K, 15K, 12K (outdoor and indoor legacy), 8K and 5K low-voltage inverters.

Closed-loop setup on each side

Closed loop means the battery's management system tells the inverter its state of charge and its charge and discharge current limits over a data cable, so the inverter charges to the battery's numbers rather than to voltage setpoints you typed in.

On the EG4 battery

The WallMount All Weather quick-start guide gives the procedure. The protocol "can only be changed with the master battery temporarily set to address 64 (all switches ON)." You restart the BMS, hold the Return key for 5 seconds to open the Protocol Setting menu, choose the protocol, then set the master battery's DIP switch back to address 1 and power-cycle it. EG4 also notes that the battery "cannot communicate with the software and a closed loop inverter simultaneously," so BMS Tools diagnostics and inverter communication are one or the other. Source: WallMount All Weather quick-start guide, v1.1.6, read October 19, 2026.

The two EG4 documents disagree on RS485. The quick-start guide lists RS485 P03-SLK for Sol-Ark; the newer user manual, v1.6.3, assigns RS485 P03 to Luxpower and lists Sol-Ark under CAN only, read October 19, 2026. On the 15K, the outdoor 12K and the 18K, Sol-Ark routes battery communication through the CAN port (below), so CAN is the path both documents agree on.

The LifePower4 V2 comes in two designs, per its quick-start guide, v1.3.1. Units with DIP switches set the protocol by switch, and code 3 is Sol-Ark over CAN. The newer design has no DIP switches and an Auto-ID feature in which "the BMS checks for inverter communication signals and automatically selects the proper protocol"; its CAN compatibility list includes Sol-Ark.

On the Sol-Ark inverter

Sol-Ark's battery setting is named BMS Lithium Batt. The 15K-2P-LV manual defines it as allowing "closed-loop communication with the tested batteries included in Sol-Ark's Battery Integration Guide." Battery communication goes through the RJ45 port labelled CAN, which per the manual "supports both Canbus protocol and Modbus protocols." The integration guide adds that the separate Modbus RS-485 port on the outdoor models and the 18K is "not for battery communications, with the exception of Storz batteries," and asks for inverter firmware "C 1.4.5.2 or greater" for reliable CANbus communication. Sources: 15K-2P-LV manual, Rev 13, July 16, 2026 and the integration guide above, both read October 19, 2026.

For its listed CAN batteries, Sol-Ark's guide sets BMS Lithium Batt to 00. It publishes no value for an EG4 battery, because EG4 is not in the guide. If the inverter is in BMS Lithium mode and hears nothing, the 15K manual's fault table lists F58: Sol-Ark "is programmed to BMS Lithium Battery Mode but cannot communicate with a BMS."

On EG4 inverters

EG4's FlexBOSS21 manual sets the battery under Battery Type and Lithium Brand: "select 'Lithium' under 'Battery Type' and then select '0:EG4' under 'Lithium Brand'" for EG4 batteries. For other brands it points to "an updated list of third-party batteries capable of closed-loop communication" on EG4's site. The list we found is published for the 18kPV, version 1.0.1, and gives a battery code per brand, among them EG4 (0), Pylon (2), Pytes (0), Fortress (18), Volthium (6) and BASCO for the SimpliPhi line (22). We did not find a separate FlexBOSS21 list. Sources: FlexBOSS21 manual, v1.3.7, read October 19, 2026.

Open-loop operation and what the makers say

Open loop means the inverter runs the battery on voltage alone, from settings you enter, with no data link. Both brands' inverters allow it. EG4 discourages it for lithium; Sol-Ark's manual describes open-loop charging without recommending against it.

Sol-Ark. The 15K datasheet lists compatible battery technology as "Lead-acid or Lithium" and footnotes that lead-acid charge settings are limited to capacity, absorption, float and equalization. The 15K manual says the inverter "can work with any battery chemistry as long as it remains within the range of 43 VDC to 59 VDC" and that "if you are not using closed-loop communications, the inverter will follow" its own charge stages. The 12K-2P and 5K-1P datasheets list battery technologies as "Lithium" only. Sources: 15K datasheet, Rev 8, September 10, 2026, 12K-2P datasheet, Rev 3, June 18, 2025, 5K-1P datasheet, Rev 3, June 18, 2025, all read October 19, 2026.

EG4. The FlexBOSS21 manual says to "Select the 'Lead-Acid' setting if the battery cannot communicate with the inverter," and in the same section that EG4 "strongly recommends using closed-loop communications between the battery bank and inverter." The LifePower4 spec sheet warns that in open loop "battery SOC% and battery voltage do not directly correlate." Source: LifePower4 48V V2 spec sheet, read October 19, 2026.

Voltage and current limits from the datasheets

All of these are 48V-class products, so the nominal voltage matches on paper. The limits that differ are the voltage window and the current ceiling.

Sources: the EG4 and Sol-Ark spec sheets and datasheets cited above, plus the 18kPV spec sheet, v1.4.3 and FlexBOSS21 spec sheet, v1.3.0, all read October 19, 2026. The 15K manual adds the 160 A single-terminal limit.

One revision matters here. EG4's current WallMount All Weather spec sheet, v1.2.1, rates the battery at 140 A continuous, and its changelog records the change at version 1.1.7: "Modified Max. Continuous discharging current from 200A to 140A." The same sheet keeps "200A (Max. Continuous for 30 min)" on discharge, and its BMS table trips on discharge over-current above 205 A after 10 seconds. The quick-start guide states the battery "is capable of charging/discharging up to 200A before the BMS shuts off the pack" and adds: "Ensure the inverter is configured to handle this high of a current, and size all wires accordingly!"

Two parts of this site rest on the older v1.0.1 sheet: our EG4 PowerPro model page and our continuous vs peak power guide use its 200 A, 10.2 kW continuous figure, where v1.2.1 rates 140 A continuous (about 7.2 kW at 51.2 V, our arithmetic), and our UL 9540 guide describes the older sheet, which named no UL standard, where v1.2.1 lists "UL1973, UL9540A (Passed)".

Our arithmetic on those figures, not a maker statement: one WallMount at 140 A already exceeds the Sol-Ark 5K-1P's 120 A ceiling, so the inverter is the limit there. Reaching the 250 A or 275 A ceilings of the larger inverters takes two units (280 A combined). EG4 also publishes a recommended minimum bank size: at least 300 Ah per 18kPV, which two 280 Ah units meet, and 600 Ah per FlexBOSS21, which takes three.

Warranty conditions that depend on the pairing

Sol-Ark excludes damage caused by unlisted batteries. The integration guide states that "The warranty does not cover damage caused by any battery that is not specifically listed" in the Low Voltage Battery Integration Guide. The 15K manual adds that damage from "improper use of the communication protocols (Canbus or Modbus) will not be covered by warranty." The 15K warranty document itself excludes "wrong voltage batteries," "Incidental or consequential damage caused by other components of the power system" and operation contrary to product instructions, and says the install verification checklist "must be filled out, signed, and dated to secure full warranty coverage." Source: Sol-Ark 15K-2P-N limited warranty, read October 19, 2026.

EG4 excludes damage from open-loop spikes; neither EG4 warranty page names inverter brands. The WallMount All Weather battery warranty is a 10 year prorated warranty and lists as exclusion 11: "Damages incurred from voltage or current spikes due to open-loop lithium battery communications." Exclusion 10 covers "Failure to update with the most recent firmware version, when known defects/issues are corrected." The battery warranty also excludes product "not purchased through an EG4 approved vendor." The 18kPV inverter warranty carries the same open-loop exclusion as its item 10. Separately, EG4's BMS terms and conditions, read October 19, 2026, void the BMS warranty if "The BMS is used with incompatible equipment or in conditions outside specified parameters," and ask that it be used with inverters "as specified in the manual," which for the WallMount includes the Sol-Ark CAN protocol. Sources: WallMount All Weather warranty and 18kPV-12LV warranty, read October 19, 2026.

Put together for a Sol-Ark plus EG4 system: EG4's battery warranty excludes open-loop spike damage, and Sol-Ark's guide gives no closed-loop setup for EG4 and excludes damage caused by unlisted batteries. Our warranties comparison covers the other battery terms.

UL 9540 system listings

UL 9540 lists an assembled system, a specific inverter with a specific battery, rather than either box alone. The plain-English version is in our UL 9540 and NFPA 855 guide.

EG4 publishes system certificates for its own pairings. Its ESS model number explanation says EG4 configurations "are certified to UL 9540 through ETL listings that pair designated combinations of EG4 inverters and batteries," and that its batteries "are listed to UL 1973 and tested to UL 9540A." The Intertek certificates posted on the WallMount All Weather product page, to UL 9540:2023 Ed.3, cover the battery with the 18kPV, the 12kPV, the FlexBOSS18 and the FlexBOSS21. For the FlexBOSS21 the configurations run from one inverter with one battery to three inverters with six batteries. The LifePower4 spec sheet says "UL9540 listed with 18kPV-12LV." Sources: EG4 ESS model number explanation, 18kPV + WallMount All Weather certificate, FlexBOSS21 + WallMount All Weather certificate, all read October 19, 2026. The current spec sheet, v1.2.1, lists the battery's own certifications as "UL1973, UL9540A (Passed)."

Sol-Ark points to its partners. The 15K datasheet's battery panel reads "Multiple UL 9540 Certifications," while its safety certification row lists UL 1741 variants, UL 1699B, UL 1998 and CSA C22.2 107.1-16. Sol-Ark's partner page describes "battery partners that support closed-loop communications and UL9540." Its product document library, read October 19, 2026, carries a UL 9540 certificate only for its commercial L3 HVR battery, and none for a residential inverter and battery pair.

So for a Sol-Ark inverter with an EG4 battery, neither maker publishes a UL 9540 system listing. Where your jurisdiction requires one, that is a permit question to settle before purchase.

What neither maker publishes

• A Sol-Ark statement naming EG4. Revision 7 of Sol-Ark's guide does not mention EG4 in either partner tier.
• The Sol-Ark-side setting for an EG4 battery. Sol-Ark gives BMS Lithium Batt values only for listed batteries.
• What EG4 validated P03-SLK against. EG4 names Sol-Ark as a brand, with no inverter models or firmware versions.
• A UL 9540 listing for any Sol-Ark and EG4 combination.
• A round trip efficiency figure for the pair. EG4's battery sheet has none, which our round trip efficiency comparison records, and a system figure would depend on the inverter in any case.
• A FlexBOSS21-specific third-party battery list. The manual points to EG4's site; the list we found there is for the 18kPV.

In both brands' hybrid systems the battery sits on the inverter's DC side, so the inverter choice and the battery choice are one decision; AC-coupled vs DC-coupled explains why that matters on a retrofit. EG4's written position covers an EG4 battery on an EG4 inverter, with UL 9540 certificates for named combinations. Sol-Ark's written position covers a Sol-Ark inverter with a battery from the Certified tier of its current guide; it describes its Proven partners as having "not yet been certified by Sol-Ark." A Sol-Ark inverter with an EG4 battery rests on EG4's documents, plus Sol-Ark's general statement that its inverters "can generally function with most 48V batteries". Makers revise these files often, so confirm the current version on your install date.