Usually only the batteries: after about ten years, most off-grid systems need new batteries, not a new system. Replace the old off-grid system only when its design no longer fits. Think of a low system voltage, controllers that cannot charge lithium, or a use that outgrew the inverter.
The generator starts in October instead of December. The inverter trips when the compressor, pump or washing machine starts, at 40% on the display. "If I have to replace the batteries after only 3.5 years it eliminates any gain," wrote an owner whose AGM bank collapsed under load.
In Hechtel-Eksel we kept the six solar panels. On a farm in St-Georges-sur-Meuse, 46.2 kWh of battery made the generator a back-up.
Which parts of an off-grid system wear out first?
The battery wears out first, then the parts that move or run hot: fans, the generator and older electronics. Solar panels and cables age slowest, so a ten-year-old system is rarely finished as a whole.
Lead batteries reach their end of life through cycling and heat. Victron designs its AGM deep-cycle batteries for 400 cycles at 80% discharge and 1,500 at 30%. Gel does a little better: 500 and 1,800 cycles.
Design cycle life at 80% discharge
Under float service, Victron gives its AGM batteries 7 to 10 years at 20 °C. At 30 °C that becomes 4 years, at 40 °C only 2. A lead battery in a warm container or under a sunny roof ages twice as fast.
| Part | What ages it | What to check |
|---|---|---|
| Battery | Cycles, deep discharges, heat, never reaching a full charge | Voltage under load, capacity test, age and type |
| Inverter-charger | Heat, dust, fans, overloads | Error log, fan noise, whether the maker still supports it |
| Charge controllers | Mostly technology, not wear | PWM or MPPT, voltage, lithium charge profile |
| Solar panels | Slow loss of output, damaged glass or connectors | Output on a clear day, cables and connectors |
| Generator | Running hours and cold starts | Hours counter, service history, auto start |
| Cables, fuses, switchboard | Heat at loose connections | Warm spots, fuse ratings against new currents |
How the parts of a professional system work together: see the components of an off-grid system.
Is it the battery, the inverter or your use that changed?
A worn battery, a tired inverter and a grown use all make the system shut down earlier. A Belgian owner of old lead batteries took the candles out again: they gave up at sunset. Only the first is solved by an off-grid battery replacement.
The battery is worn
The voltage collapses when a big load starts, and the battery is empty long before the display says so. "It is not the 70-80% capacity that stops its use," a forum member wrote. "It is the inverter shutting down under heavy load due to battery voltage slumping," he added.
The inverter is tired
Overload or temperature alarms at loads it used to carry, loud fans, or faults that come back. An inverter the manufacturer no longer supports is hard to connect to a modern battery.
Your use has grown
A new cold room, a heat pump, a milking robot, an electric vehicle or more people on the site. The system is not old but too small: a new battery empties just as fast, only later in the day.
From symptom to the right fix
Tip
Before you replace anything, write down what changed on your site since the installation: new machines, more people, longer opening hours. That list decides more than the age of the parts.
Can you replace lead-acid batteries with lithium off-grid on your existing inverter?
Often yes: a lead to lithium conversion works when four things fit. The system voltage, the charge settings of every charger, the communication with the battery and the room temperature. Victron inverter-chargers and chargers work with lead and, with the right settings and communication, with many lithium batteries.
The voltage must match
Many older systems run at 12 or 24 V; many stationary lithium batteries are built for 48 V. A Belgian forum owner was advised to buy 48 V modules, until someone noticed his 24 V PWM charge controller. He replaced it with an MPPT model, and the inverter as well.
Every charger needs a lithium profile
The inverter-charger, each solar charge controller and any other charger get the lithium settings. In a Victron Community thread on a 20-year-old lead bank going to lithium, the advice was clear: set the limits in every charging source.
The battery must talk to the system
Victron connects the battery management system to the inverter and chargers, mostly over a CAN bus via a GX device. It publishes a list of tested batteries. Some self-built battery management systems cause confusing alarms, such as overload warnings with hardly any load.
Mind the cold
According to Victron's datasheet, its LFP batteries discharge from -20 °C but only charge from +5 °C. A battery in an unheated barn or container needs heating or a warmer place.
Why LFP is the usual lithium chemistry for stationary storage in a business: see our article on LFP, NMC and sodium-ion.
When should you replace an old off-grid system, not only the battery?
When the old design is the real limit, not the age. An inverter that is still supported, has no recurring faults and carries your largest start can stay. Otherwise an off-grid inverter replacement or a full off-grid system upgrade follows.
| Your situation | Usually the best choice |
|---|---|
| Battery worn, inverter supported and big enough, use unchanged | New battery only, with lithium settings and communication |
| Battery worn, inverter trips at starts that are new on the site | New battery and a bigger inverter, or a soft starter on the new machine |
| 12 or 24 V system with PWM controllers | A new design at 48 V with MPPT charge controllers; keep the panels where they are sound |
| Use has doubled since installation | A new design, sized on your current use and on January |
| Generator runs far more than planned | More battery and more panels first, then look at the generator |
| Single-phase system, three-phase machines now needed | Three inverters for a 3 x 400 V grid, one per phase |
At 48 V, the same power needs half the current of 24 V, so cables and fuses stay manageable when the system grows. Machines with heavy starts, such as compressors and welders, decide the inverter size: see an off-grid workshop with compressors and welders.
Our verdict
A ten-year-old system with a supported inverter and an unchanged use needs a new battery, set up properly. Buying the same lead again buys the same problem in a few years. A system at 12 or 24 V, with PWM controllers or far more load than planned is better redesigned, keeping sound panels and the generator.
What happens to the solar panels and the generator?
The solar panels usually stay; the generator stays too, but becomes the back-up it was meant to be once the battery is large enough.
Check the panels on a clear day: output, cables, connectors and glass. With modern MPPT charge controllers or a hybrid inverter, sound panels stay and new ones go next to them.
In Hechtel-Eksel a hybrid Victron now works as solar inverter and battery charger. Six panels suffice: the meditation centre mainly uses power at weekends and charges during the week.
A fully off-grid home in As combines solar panels, a 30.8 kWh battery system with 24 kVA of inverter power and a propane generator. On the farm in St-Georges-sur-Meuse, the generator that ran day and night is now only a back-up. Auto start and generator sizing: see a generator with a battery off-grid.
Which rules apply when you renew an off-grid system?
The AREI applies with or without a grid connection. An important modification or extension needs a conformity inspection by an approved body before the installation is used again, for homes and businesses.
The FPS Economy gives examples: a change to the earthing system or a non-identical replacement of a distribution board is important. An identical replacement is not; you update the schemes and documents, and the next inspection checks them.
A switch from lead to lithium with a new inverter or a new system voltage is not an identical replacement. Ask an approved body whether it counts as important, and plan the inspection in your renewal.
Connected to the grid in any way, for example as a charger? Then the grid rules apply too. A Belgian semi-off-grid owner failed his technical inspection: his inverters and traction batteries were not on the Synergrid list.
Under the EU Battery Regulation, every industrial battery above 2 kWh placed on the market from 18 February 2027 needs an electronic battery passport. Ask your supplier when you order.
Old batteries must be handed in for recycling: see old lithium batteries in a business. Whether a used battery is a good idea: see second-life batteries.
Send us the age, type and rating plates of your battery, inverter and chargers, and we will tell you what to keep and what to renew.
How do we renew an older off-grid system?
We start from what you have and use today, not from a new kit, for a farm, a business building or a home.
- Step 1: You send us the age and type of the battery, the inverter, the charge controllers and the generator, with photos of the rating plates and any logs.
- Step 2: We compare your current use with the design use, and measure where possible. That shows whether the battery, the inverter or the design is the bottleneck.
- Step 3: We propose what stays and what is renewed: sound panels, generator and cables stay; battery, settings and communication are designed as one system.
- Step 4: We install, set every charger, and have the installation inspected where the modification requires it.
- Step 5: You follow production, storage and use in real time with our monitoring software, so you see the next problem coming instead of noticing it in the dark.
We connect new batteries, revise installed ones, and maintain and repair battery systems. A good service agreement: see warranty and maintenance of a business battery. More about our off grid accu and off-grid systems for businesses, farms and homes.
Frequently asked questions
How long does a new lithium battery last in an off-grid system?
Victron gives its LFP batteries 2,500 cycles at 80% discharge, 3,000 at 70% and 5,000 at 50%, with at least 80% capacity left. The years depend on your daily discharge depth; our guide on the off-grid battery works it out.
My lead batteries lasted almost 20 years. Why switch?
Gently cycled, cool lead banks can last very long: one forum owner ran a large 24 V bank for nearly 20 years. Most do not. Lithium gives far more cycles and, as a cabin owner who left AGM found, wastes no winter sun on the long final charge of lead.
Should I go from 24 V to 48 V when I renew?
Usually yes, if the system grows or must carry heavier machines. It often means new charge controllers and a new inverter, so it belongs to a redesign, not to a battery swap.
Can I keep my old lead batteries as a reserve next to the lithium?
No: do not mix old lead and new lithium in one bank or keep the old bank connected. The chemistries charge at different voltages, so the old batteries pull the new ones down. More in our guide on which off-grid battery you need.
Is your off-grid system due for renewal?
Send us the age and type of your battery, inverter and chargers, with photos of the rating plates. Tell us what changed on your site. One of our engineers tells you honestly what can stay and what must go.
Sources
- Victron Energy: GEL and AGM batteries datasheet
- Victron Energy: Lithium Battery Smart datasheet
- Victron Energy: battery compatibility
- FPS Economy: inspection of non-domestic electrical installations (FR)
- FPS Economy: inspection of domestic electrical installations (FR)
- Regulation (EU) 2023/1542 on batteries and waste batteries, Article 77
- Victron Community: change a big lead battery in an off-grid system to LiFePO4
- Victron Community: why have my solar PV batteries failed so soon?
- DIY Solar Forum: LiFePO4 end of life at 70% capacity
- BricoZone: replacing lead batteries with LFP (FR)
- DIY Solar Forum: our off-grid cabin Victron setup