Accessories for batteries

Base plates, wall brackets and floor stands

Stacked modules need a defined foot and a defined restraint. A base plate spreads the load, sets the stack level and usually carries the earthing point and the cable entry. A wall bracket ties the top of the stack back to the structure so it cannot topple, which matters because a high voltage tower can pass 200 kg once it is full. A floor stand is used where the wall cannot take the load or where the pack sits away from a wall.

• Base plate: brand specific and module specific. It fixes the stack pitch, so a plate from another series will not accept the modules even if it looks similar.
• Wall bracket: the anti-tip element. Check the fixing against the wall material, since plasterboard and aerated block need chemical or through fixings.
• Floor stand: for free-standing or garage installations, and for cases where the wall is a facade with insulation and no load-bearing layer behind it.
• Clearances: leave the manufacturer's stated gap around the stack for ventilation and for service access to the terminals.

BMS, controller units and expansion modules

The BMS (battery management system) monitors cell voltage and temperature, balances cells, enforces charge and discharge limits and reports SoC (state of charge) to the inverter. On modular packs it is often a separate top or base unit, sometimes called a control module, power control unit or master module, and one is required per stack. The individual modules under it hold cells only.

• One controller per stack: adding modules does not mean adding controllers, but exceeding the maximum module count means starting a second stack with its own controller.
• Expansion modules must match the existing modules in type, capacity and, in practice, in age. Mixing an old and a new module in one string means the whole string works to the weakest cell group.
• Firmware: after adding a module, update the BMS and the inverter so the new capacity is recognised and the balancing algorithm covers it.
• Monitoring: the controller is also what feeds the monitoring portal with cell data, so a missing or unconfigured unit means no visibility.

Communication cable: CAN or RS485 and why the pin-out matters

The battery and the inverter exchange voltage, current, temperature, SoC and permitted charge and discharge limits over a serial link. Two physical layers dominate. CAN (usually CAN 2.0B at 500 kbit/s) is the more common choice on modern high voltage packs and carries a structured message set. RS485 (Modbus RTU) appears on many low voltage 48 V systems and on older equipment. Which one applies is decided by the pairing, not by the installer.

The connector is almost always RJ45, and that is exactly the trap. The housing is standard, the pin assignment is not: one manufacturer puts CAN High and CAN Low on pins 4 and 5, another on pins 1 and 2, and a third uses the same socket for RS485. A standard Ethernet patch lead will physically click into place and communicate nothing, or in the worst case put voltage on the wrong pin. Use the cable supplied with the battery or the manufacturer's replacement part, keep the run short, route it away from DC power cables and set the address DIP switches and the terminating resistor as the manual states.

Power cables, busbars, terminal torque and DC protection

Power cabling between modules is supplied as a matched set with the right cross section, the right length and factory crimped lugs. On tower packs the modules are often joined by rigid busbars instead of cable. Both carry the full pack current, so a poor joint is a heating problem long before it is an electrical one.

The battery circuit also needs its own protection and its own isolator, sized for DC rather than AC. An AC-rated device in a DC circuit cannot reliably break the arc, because there is no zero crossing to help extinguish it. Use a purpose-made DC breaker or a fuse and holder rated above the pack's maximum voltage and matched to the inverter's maximum battery current.

• Cross section follows current, not preference. A 48 V pack draws roughly four times the current of a 400 V pack for the same power, so low voltage systems need noticeably heavier conductors and shorter runs.
• Torque: tighten every terminal with a calibrated torque wrench to the value printed in the manual, typically in the range of 2 to 8 Nm depending on the bolt size. Under-torqued joints arc and overheat, over-torqued ones strip the thread or deform the busbar. Re-check at first service, since bolted joints relax after thermal cycling.
• Polarity and sequence: connect in the documented order, usually communication first, then DC, then switch on. Reversed polarity on a battery input is not a recoverable mistake.
• DC breaker or fuse: rated voltage above the highest pack voltage, rated current above the continuous working current and below the cable rating. Consumables and enclosures for the DC side sit in electrical installation material.
• Isolator: a visible, lockable disconnect between the battery and the inverter, required for safe maintenance and for firefighter access.
• Earthing: bond the enclosure, base plate and stack frame to the main earthing terminal with the specified conductor. This is a protective function, and it is also what makes insulation monitoring in the inverter behave correctly.
• Surge protection: where the DC run is long or leaves the building, a Type 2 DC surge arrester on the battery circuit is sensible practice.

Backup boxes, transfer switches, sensors and enclosures

A backup box is the AC-side accessory that gives a hybrid system a working island when the grid fails. It contains an automatic transfer switch that disconnects from the grid within milliseconds, keeps the inverter's off-grid output isolated from the network so no voltage is exported to a dead line, and reconnects once the grid is stable again. It is what turns a self-consumption system into a backup system.

• Whole-house backup puts the entire consumer unit behind the box. Simple to live with, but every load then has to fit under the inverter's off-grid power rating.
• Partial backup feeds a separate backup distribution board with selected circuits: lighting, sockets, boiler, freezer, heating pump. Cheaper and far easier to size correctly.
• Temperature sensors let the BMS derate or stop charging in the cold. Charging a LiFePO4 pack below 0 °C is what damages cells, so this is a protective part, not a convenience.
• Enclosures with a stated IP rating extend siting to garages, outbuildings and outdoor walls. Check the rating and the operating temperature window together, since an IP66 box does not keep a pack warm.

Quick accessory comparison

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