Had issues with 10yr+ installation. 1 inverter going into alarm mode, unable to access monitoring apps and wanted someone to review and document worthiness of the 2 systems I have. As you will find with older systems, the original installers have moved on, other companies only want to replace and install new, or make up silly prices as they don't want the work, so struggling for 18 month plus trying to source someone to do this. Ronald managed to fit me in the day after contact as he was in the area. Spent a couple of hours on site, found issue with the inverter alarm and he monitoring this to find a total solution, got me back onto the monitoring apps, provided a report on the installations and identified potential areas of concern. These are the people you need for diagnostic reviews of your installations, long term industry professionals, who have a wealth of knowledge gained through working in the industry, know the differing systems and how to contact and approah the companies involved. These are the people you need if you are having issues with installers and / or product and/or supply companies.
Add an extra battery to your existing solar system
- No new inverter needed (usually)
- Must match existing battery brand
- Check monitoring data first
Before spending on an extra battery, review your monitoring data. If your battery regularly fills to 100% and exports excess, or regularly drains before morning rates start, a second unit will help. If neither pattern is present, expanding capacity may not improve your self-consumption. Where an expansion does stack up, it is from £995 all-in fitted.
Book a compatibility assessmentWhat's in a health checkBig thanks to Ron. He was incredibly patient and helpful over the phone, taking the time to walk myself and the installer through every troubleshooting step. Through lots of testing he figured out the issue was definitely a hardware issue, which allows us to consider our next steps. Support fees are clear and they operate a “no fix no fee” policy. It is rare to find that kind of honesty combined with dedicated phone support nowadays. I highly recommend Ron, if you need help with your solar system don’t hesitate to give him a call.
Great advice from Ronald at Solar Tech Support, got my inverter back on line and stable.
We reached out to Solar Technical Support after our solar energy system stopped working. As GivEnergy 'solar orphans,' we have been extremely pleased with the service from STS - our system was back up and working within a day of us contacting them. We found other solar engineers reluctant or unable to help us, so it has been great to find this organisation. We would definitely use them again and would recommend them to anyone, especially GivEnergy orphans!
Ronald was great to help me sort out my giv energy inverter issue since company has gone bankrupt in april 26.
Ronald tried to help solve a fault with communications between battery and inverter. Whilst in the end a hardware fault was diagnosed and not possible to fix remotely his attempt to fix and guide me through steps to fault find were appreciated. He was available at a time convenient to my availability. Great service for anyone requiring independant tech support for their solar or battery system.
This guide is for systems that already have a battery. If you have solar panels but no battery at all, see the add battery to existing solar guide — that covers AC vs DC coupling, inverter compatibility, and costs for a first battery installation. This page covers expanding an existing hybrid battery system by adding a second or third battery module.
When does adding an extra battery make sense?
An extra battery increases your usable storage capacity. Whether this improves your bill savings depends on whether your current battery is actually a limiting factor. Check your monitoring portal for these patterns before deciding.
How to check your data: Log into your inverter monitoring portal (GivEnergy portal, Sunsynk portal, Growatt ShinePhone, the FoxCloud 2.0 app, etc.) and review the battery charge graph for a recent summer week. If the battery hits 100% before 2pm on sunny days, more storage capacity would allow you to capture that excess solar. If the battery never fills up, the constraint is generation rather than storage.
Battery expansion compatibility by brand
Most hybrid inverters support multiple batteries, but the maximum capacity varies. The new battery must be the same brand and compatible series as your existing battery — mixing brands is not supported.
AIO 2.0 kW
Supports up to 2 x 2.6 kWh = 5.2 kWh total. Additional battery: GivEnergy 2.6 kWh unit.
AIO 2.6 kW
Supports up to 2 x 4.8 kWh = 9.5 kWh total. Additional battery: GivEnergy 4.8 kWh unit.
AIO 5.0 kW
Supports up to 4 x 4.8 kWh = 19.2 kWh total. Up to 3 additional batteries possible.
GivEnergy Gen2 / 3-phase
Check model specs — typically supports 2–4 batteries. GivEnergy Ltd is in administration, so confirm the limit with your installer or an independent engineer from the unit's model and firmware version.
Sunsynk Hybrid 3.6–8.0 kW supports multiple Sunsynk/Pylontech compatible batteries. The Sunsynk inverter communicates with batteries via CAN bus — compatible Pylontech batteries (US2000, US3000) are officially supported alongside Sunsynk's own units. Total supported capacity varies by model — check the Sunsynk compatibility guide for your inverter model.
Growatt SPH series supports multiple Growatt GBLI battery units — typically stackable up to 30 kWh. SolaX X1/X3 Hybrid G4 supports up to 4 Triple Power 5.8 kWh batteries (up to 23.2 kWh). In all cases, use the inverter manufacturer's specified battery brand and model.
- ECS stacks
- One master and up to 6 slaves on the H1/AC1 and H1-G2/AC1-G2, and one master and 2 to 6 slaves on the H3/AC3. The H3 Pro takes more. The H3 Plus takes Fox's CQ batteries only, not ECS.
- EQ stacks
- On the H1-G2 and H3/AC3: EQ3300 and EQ5000 up to one master and 5 slaves, EQ6000 Plus up to one and 6, EQ4800 and EQ5500 up to one and 8.
- EP batteries
- Up to 4 in parallel through a Fox junction box. Fox ESS UK lists up to 8 with the H3 Pro.
- After adding
- Fox advises a firmware update after adding batteries, and advises against adding more than 2 years after commissioning. Cover may be refused for an install outside its configuration guide.
Fox ESS lists which of its own batteries each inverter takes, and how many, in its Inverter & Battery Configuration Guide, so your installer checks that guide for your model. Fox's manuals are on our Fox ESS documents page, and our Fox ESS hub covers the range. If an alarm shows after adding a battery, see Fox ESS BMS communication fault. If the battery won't charge, see Fox ESS battery not charging.
Check before purchasing: Battery compatibility depends on the battery model and its version, as well as the inverter model. For Fox ESS, the version is shown by the battery's serial number, and Fox advises a firmware update after adding batteries. Before ordering, confirm the compatible battery model with your installer, or with the inverter manufacturer where that manufacturer is still trading. GivEnergy Ltd went into administration in April 2026, so there is no GivEnergy manufacturer desk to check with; a GivEnergy compatibility question goes to your installer or an independent engineer. Using an incompatible battery can cause BMS communication faults and may void warranties. If in doubt, book a compatibility assessment before purchasing hardware.
What the installation involves
Adding an extra battery typically takes 2–4 hours on-site. The process is straightforward on most well-installed systems.
Confirm your inverter model and your current battery model. For Fox ESS, also check the battery's version type (from its serial number) against Fox's battery matching guide, and the module limit against its configuration guide. Firmware comes afterwards: Fox advises an update after adding batteries. Source the correct additional battery unit from an approved distributor, your installer, or the inverter manufacturer where they are still trading. GivEnergy Ltd is in administration, so GivEnergy modules now come from remaining distributor and reseller stock rather than the manufacturer. Check that the space for mounting the new unit is available, clean, dry and ventilated, with the clearances the maker's manual asks for.
Before connecting the new battery, the engineer safely de-energises the entire system in the correct order: the battery off at its own power button first, then the AC isolator, then the PV DC isolator, and the battery DC isolator or MCB last, so it is never switched under load. Some batteries have no separate power button: on those the module switch or isolator is the battery's only control, and it still comes first. Our order for a Fox ESS system is the battery's power button first, then the AC isolator, then the inverter's DC isolator, and the battery's DC MCB last if it has one, so the MCB is never switched under load. To turn it back on, go in reverse: battery DC MCB, DC isolator, AC isolator, then the battery's power button. Read the full shutdown guide. Connecting or disconnecting batteries on a live system can cause equipment damage and arc flash risk. Always carried out by a qualified engineer.
The new battery unit is mounted on the wall or placed on the floor (depending on model). On makes that are wired in a bank, the DC bus connection is made from the existing battery bank to the new unit using manufacturer-supplied cabling, and the new battery is added to the series or parallel configuration as specified by the inverter manufacturer. Never mix series and parallel wiring without specific guidance. For Fox ESS batteries the engineer follows Fox's manual for that battery. ECS and EQ modules stack on the existing ones and join the same series stack, with no separate DC cabling to the new module. EP batteries are wired in parallel through a Fox junction box. Fox's battery matching guide sets which battery types can share a stack, and its configuration guide sets how many your inverter takes.
On makes that chain a CAN cable from battery to battery, the CAN bus communication cable is extended from the existing battery to the new unit. This is how the inverter coordinates charging across both batteries, monitoring individual state of charge and balancing the charge/discharge between units. The CAN bus termination resistor must be moved to the last battery in the chain. On GivEnergy LV battery systems the link is RS485 rather than CAN, and there is no terminator to move. On Gen 2 and Gen 3 batteries one plug-in cable carries power and comms; Gen 1 batteries have power on cable lugs and a separate data cable on a green pin connector. Each battery's address is set on dip switches. On Fox ESS ECS and EQ batteries the inverter's CAN cable stays on the master module only, and the new module needs no CAN cable of its own. On Fox ESS EP batteries the new unit is chained to the last one with Fox's link cable, and the end plug moves to the new last unit.
The inverter portal is updated to reflect the new total battery capacity. On GivEnergy systems, this involves updating the battery number and capacity in System Settings. The inverter must recognise the new total to calculate state of charge correctly. Without this update, the displayed percentage will be inaccurate and scheduled charge/discharge windows may not work as expected.
The system is re-energised in the order for that make. On GivEnergy that is AC isolator on, PV DC isolator on, battery DC isolator or MCB closed, then the battery switched on at its power button. On Fox ESS it is the reverse of the shutdown in step 2. A charge cycle is initiated. On makes that report each battery separately, verify both batteries appear in the monitoring portal, the total capacity displayed matches the expected new figure, and both units discharge in a coordinated manner. On Fox ESS, check the new total capacity and state of charge in the FoxCloud 2.0 app or on the inverter. An ECS or EQ stack shows as one battery, not two, and the web portal does not show the battery. A post-installation report documents the configuration and test results.
What does an extra battery cost?
Our price is all-in fitted: battery hardware, delivery, installation, and portal configuration.
Mounting, DC connection, CAN bus, inverter configuration, test, and post-install report, all included in the all-in fitted price.
All-in fitted, hardware and installation. The exact figure depends on the battery model and capacity. Quoted in writing before work begins.
When to add one. Every month you export excess solar or import expensive daytime electricity instead of storing it is a cost. Run the numbers for your specific usage patterns before deciding when to act. On Fox ESS, Fox advises against adding batteries more than 2 years after commissioning, so check your commissioning date.
DNO notification for battery expansion
Your installer must tell your Distribution Network Operator (DNO) when a battery is added. The route depends on your existing connection. If the total stays within 16 A per phase, a G98 notification within 28 days is enough, with no approval. Above that, G99 applies and the DNO has to agree first: a Fast Track answer is due in 10 working days and the standard route can take up to 45 working days. A battery set up to run the home in a power cut (island mode) can't use the Fast Track, so it goes through the standard G99 process. More kWh on the same inverter does not by itself change your registered kW. Your installer should handle this paperwork as part of the installation.
If your system has an export limit set by your DNO (common in areas with network constraints), adding battery storage does not automatically allow more export. Your inverter's export cap is a separate setting enforced by the inverter. Adding battery capacity may change how much power your system wants to export at peak generation — if near your export limit, discuss with your installer whether any export limit changes are needed.
Related guides
No battery at all? This guide covers adding a first battery to an existing solar-only installation.
See how to add a first batteryMore battery capacity also means longer EPS runtime during grid outages. Add backup power alongside your expansion.
See EPS installationBefore adding a battery, ensure your existing system charges correctly overnight.
See GivEnergy battery not chargingSee what to check if your Fox ESS battery isn't charging before you add another.
See Fox ESS battery not chargingSee what a battery alarm means, including one that shows after adding a battery.
See Fox ESS BMS communication faultFull overview of solar system upgrade options — EPS, bird mesh, inverter replacement, and more.
See all upgradesAdding an extra battery — frequently asked questions
Ready to expand your battery storage?
We confirm compatibility, source the correct hardware, and install to manufacturer specification — from £995 all-in fitted. Written quote before work begins. Post-installation report included.
- Compatibility confirmed before hardware is ordered
- CAN bus, DC connection, inverter config — all included
- DNO notification handled as part of installation
We’re busier than ever. Thank you for your patience.
Due to unprecedented demand we’re currently only carrying out on-site work in Yorkshire, and replies are taking up to 7 days. Remote diagnostics continue for the whole UK as normal.
Every message is read and answered, so please don’t send it twice; that only slows the queue.
We use cookies to measure traffic and ads, sharing limited hashed data with Meta and Google. Decline keeps only essential cookies. Privacy policy
Got a solar fault or need a quick answer? Drop us a message and we usually reply within a few minutes. Mon–Fri, 9am–7pm.