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Get Free Quote

More storage. More flexibility. More control over the energy your solar system produces.

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It might not be capacity at all

Before you buy modules, rule out the things that look identical to an undersized battery and cost nothing to fix.

batteryinstall.ie / expansion

Empty by ten o'clock?

That's not a fault. It's a battery sized for a smaller life than the one you're now living. Whether you can simply add modules comes down to six things — stack headroom, module matching, age gap, firmware, availability, and whether the real constraint is capacity at all.

Your existing battery

On the label on the front or side of the module.
2 modules
Age gap between old and new modules is the thing people don't expect, and it matters.

What's actually wrong

These are different problems with different fixes, and getting this wrong is the most expensive mistake in expansion.
5.0 kW — on the inverter label. If you don't know, leave it.

Verdict —

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Pick your battery brand and we'll tell you where you stand.

Now

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Current usable.

Room for

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Extra modules.

Could reach

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Full stack.

We test the existing pack before quoting. No point adding good money to a tired battery.

What we'd check before quoting

Stack limits change. The figures here are typical for each platform, not gospel — manufacturers revise them with firmware, and some older series are discontinued. We confirm against your exact model before anything is ordered.

1
If the battery is set to charge 02:00–04:00 but your tariff’s cheap band runs 23:00–08:00, you’re getting two hours of charging instead of nine. The symptom — empty by ten in the evening — is exactly what a too-small battery looks like.
2
The battery can’t see your consumption accurately, so it discharges at the wrong times or refuses to discharge at all. Very common, and invisible without checking.
3
Many systems are commissioned with a reserve — sometimes 20% or more — held back for backup. If backup isn’t configured, that’s capacity you own and can’t use, sitting idle.
4
New EV, new heat pump, someone working from home, an extension. In that case the battery isn’t faulty and isn’t mis-set — it’s correctly sized for a household that no longer exists. That’s the case where expansion is the right answer.
5
After five to eight years, some capacity loss is normal and expected — typically 10–20% on LFP. Significantly more than that, especially with cell imbalance, is a warranty conversation rather than an expansion one.

The [fault triage wizard](/faults/) walks through all of these in about five minutes. Run it before you spend anything.

What expansion actually costs

Expansion is not proportionally cheaper than buying the capacity up front, and customers are often surprised by that. You’re paying for a second visit, second commissioning, sometimes new cabling and protection, and modules at current prices rather than the prices you paid three years ago. Expect roughly [ X% ] more per kWh than the same capacity bought originally.

Where expansion clearly wins: the original battery is healthy, still supported, and the manufacturer permits matching modules. Where it usually loses: the platform is discontinued, the generation has changed, or the inverter caps total storage below what you need.

The expansion ceiling nobody mentions

Every hybrid inverter has a maximum supported storage capacity, and it’s often lower than the battery platform’s own maximum. You can hit the inverter’s ceiling with the battery only half expanded. That’s the point at which expansion stops being an option and the conversation becomes about a second system or a replacement — and it’s the single most useful thing the checker above tells you.