FOX ESS CQ7-S - LiFePO4 expansion battery module 7.02 kWh.

FOX ESS CQ7-S is a 7.02 kWh LiFePO₄ battery module intended for expanding the capacity of an already assembled CQ series system. The letter S denotes a slave role: the module adds energy but carries no control electronics of its own. Voltage 57.6 V, weight 50 kg, dimensions 660 × 360 × 190 mm, IP65 protection, 120-month warranty.

Important before ordering

This module does not work on its own. The system needs a CQ7-M master module, which handles communication with the inverter and charge balancing. If you are building storage from scratch, your order must include one CQ7-M plus the required number of CQ7-S units.

If the system is already installed and the master module is in place, it is simpler: you buy only CQ7-S modules, exactly as many as the missing capacity requires.

Why expanding beats over-buying

A common design-stage mistake is buying capacity 'to grow into'. The logic sounds sensible but works against the owner for two reasons.

First, a battery sitting underused still ages by the calendar. Paying for 28 kWh while using 10 every day means paying for service life that burns away unused.

Second, over a few years the price per kilowatt-hour usually falls while specifications improve. Buying the second half of the system later often turns out cheaper than the same capacity today. The modular CQ architecture is designed for exactly that: buy for current consumption, extend as the need arises.

What each added module delivers

One CQ7-S adds 7.02 kWh of usable energy. In household terms that is roughly another night of running a refrigerator, lighting, boiler and router, or several hours of powering a heavier load such as an air conditioner or a pump station.

It is important to understand that adding modules increases the energy reserve. The maximum power the system can deliver at any instant is set by the inverter, so adding batteries will not turn a domestic installation into an industrial one — it extends how long autonomy lasts.

Standardisation as a practical advantage

The expansion module is physically identical to the master: same dimensions, same weight, same mounting method and the same IP65 rating. For the installer that means predictability — the rack or wall structure is designed once for a single size.

IP65 protection allows the whole stack to sit outside the living envelope: in a garage, an outbuilding or under a canopy. Natural-convection cooling with no fans means silence and no servicing. The 6000-cycle rating and IEC 62619, UN 38.3 and CE certification match the master module exactly.

On mixing old and new modules

If you are expanding a system that is already several years old, bear in mind that new and worn modules in one stack perform to the weakest element. It is not forbidden, but the capacity gain will be smaller than it looks on paper. Ideally, add modules during the early years of operation while the difference in remaining life is still small.

Unsure how many modules to add, or whether you need a master unit? Tell us what is installed now and what is falling short — we will suggest a configuration and warn you if buying more will not give the result you expect.