Checked as a bank of 2 packs, which is the smallest number that accepts this inverter’s 250 amp charge current. Fewer packs still run the system, with the charge rate capped in inverter settings.
Full specifications: EG4 FlexBoss21 and BigBattery Etheron 48V 15kWh.
The four checks
Voltage window: Overlapping window 44.8 to 58.4 V
The inverter operates from 40 to 60 volts and the battery cuts off outside 44.8 to 58.4 volts. Both stay inside 44.8 to 58.4 volts, which covers a normal LiFePO4 charge and discharge cycle with margin at both ends.
Charge current: 250 A into a 300 A limit
The inverter tops out at 250 amps and the battery accepts 300 amps, so a default install cannot overrun the pack. Adding batteries in parallel raises the accepted current further.
Surge rating: Battery surge figure unpublished
A surge to 18000 watts draws roughly 375 amps at 48 volts. This battery publishes a 500 amp continuous rating and no separate surge figure, and continuous is the wrong number to check a motor start against. Confirm the peak rating and its duration with the manufacturer before running motor loads.
Closed-loop communication: Both speak CAN, RS485, no document names the pair
The inverter and the battery both support CAN, RS485. Neither manufacturer publishes a document naming the other unit, and a shared bus standard is not a shared message format. It may well work on the bench. Confirm the protocol setting with both manufacturers before relying on BMS control.
What this means when you install it
Set the inverter charge current to 250 amps or less. That is the inverter maximum, which this bank can absorb. Protect the battery run with a 350 amp Class T fuse and two parallel runs of 2/0 cable wired to a busbar rather than daisy chained, so all 2 packs share current evenly.
The inverter and the battery both support CAN, RS485. Neither manufacturer publishes a document naming the other unit, and a shared bus standard is not a shared message format. It may well work on the bench. Confirm the protocol setting with both manufacturers before relying on BMS control.
Figures side by side
| Field | EG4 FlexBoss21 | BigBattery Etheron 48V 15kWh |
|---|---|---|
| Voltage window | 40 to 60 V | 44.8 to 58.4 V |
| Charge current | 250 A delivered | 300 A accepted (2 packs) |
| Peak draw | 18,000 W surge | surge unpublished |
| Usable capacity | n/a | 30.72 kWh (2 packs) |
| Comms | CAN, RS485 | CAN, RS485 |
Manufacturer documents
Manufacturer documents: EG4 product and document library. Figures here should be read against the revision that covers your serial number, because manufacturers revise specifications without changing the model name.
Manufacturer documents: BigBattery product manuals. Figures here should be read against the revision that covers your serial number, because manufacturers revise specifications without changing the model name.
Both units, current pricing
Prices on these move week to week, and the battery is usually the line item worth watching.
EG4 FlexBoss21 on AmazonBigBattery Etheron 48V 15kWh on AmazonComms cableAffiliate links. As an Amazon Associate this site earns from qualifying purchases, at no extra cost to you. Prices and stock change often, and a listing appearing here is not a statement that the pairing above is approved.
Other pairings for the BigBattery Etheron 48V 15kWh
EG4 6000XP with BigBattery Etheron 48V 15kWh
Partial match, some fields unverified.
EG4 18KPV with BigBattery Etheron 48V 15kWh
Partial match, some fields unverified.
Sol-Ark 12K with BigBattery Etheron 48V 15kWh
Partial match, some fields unverified.
Sol-Ark 15K with BigBattery Etheron 48V 15kWh
Partial match, some fields unverified.
Questions people actually ask
Will the EG4 FlexBoss21 work with the BigBattery Etheron 48V 15kWh?
Partial match, some fields unverified. Checked as a bank of 2 packs, which is the smallest number that accepts this inverter’s 250 amp charge current. Fewer packs still run the system, with the charge rate capped in inverter settings. The four checks below show which field produced that result.
What does this pairing cost to wire up?
Beyond the two units, a 350 amp Class T fuse and holder, two parallel runs of 2/0 battery cable cut to matched lengths, and a busbar if you are running 2 packs. A comms cable if you intend to attempt closed loop, and the pinout is rarely the same between brands.
Where does this pairing go wrong in practice?
The inverter and the battery both support CAN, RS485. Neither manufacturer publishes a document naming the other unit, and a shared bus standard is not a shared message format. It may well work on the bench. Confirm the protocol setting with both manufacturers before relying on BMS control.
What charge current should I set?
The inverter tops out at 250 amps and the battery accepts 300 amps, so a default install cannot overrun the pack. Adding batteries in parallel raises the accepted current further.