Guide · Battery Systems · Technical

How home battery storage works chemistry, cycles, and the inverter's role

Q: Can I increase the SoC upper limit to 100% to get more usable capacity?

Yes, most systems can be reconfigured to charge to 90% or 100%. The trade-off is accelerated degradation — charging to 100% every cycle ages the battery 30–40% faster. Most installers default to 80% because the extended lifespan is worth the 20% capacity reduction. For seasonal use (winter when solar is limited), you can temporarily increase to 90% or 100% then drop back to 80% in summer. Check with your installer whether your system supports this flexibility.

Q: Is my battery safe if it shows high temperature warnings?

The BMS will automatically disconnect the battery if internal temperature exceeds ~60°C to protect the cells. Temperatures above 60°C dramatically accelerate chemical degradation and increase thermal runaway risk. If you see temperature warnings in your portal, investigate: is the battery in direct sunlight? Is ventilation blocked? Is the room temperature consistently very high? These are correctable installation issues. Contact your installer to consider relocating the battery if necessary.

Q: What happens if I fully drain the battery every day?

100% DoD cycles daily will degrade the battery significantly faster — expect 30–50% capacity loss within 5–7 years instead of 10+. The BMS will cut off discharge around 5–10% SoC to prevent over-discharge damage, so you can't truly reach 0%. If your load genuinely requires deep cycles, you can configure the system to allow it — just accept the shorter battery life. Most UK domestic users don't need deep cycles: daytime solar generation typically meets the load, and overnight use is moderate.

Q: Should I be concerned if battery health drops 5% in the first year?

A 3–5% drop in year one is normal — lithium batteries experience burn-in degradation in months 1–6 as cell chemistry stabilises. After that, degradation should settle to roughly 0.5–1% per 100 cycles. If health continues dropping rapidly after year one (5%+ per year), investigate: the battery may be cycling at unusually high depth, running too hot, or the BMS may be misreporting capacity. A remote health check will identify which.

A battery is not a black box. Understanding how it charges, discharges, and ages helps you configure it correctly and diagnose problems when things go wrong. This guide covers lithium chemistry, the BMS, charge cycles, efficiency loss, and why your system limits SoC.

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Rated 5.0 on Google Read all 73 reviews

My Givenergy system went offline, so I lost control of it. Ron from STS and Craig from Norfolk Solar were most helpful in diagnosing the problem by phone. Full marks for their patience and ability.

Tony Jackson · Jul 2026 Google

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration. So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026

A superb service from Ron who went beyond the normal service received from other Tech support companies. I live abroad and was badly let down when my givenergy system failed (and the company went bankrupt) and the local supplier ran away from the problem. Ron sorted the problem and even accessed specialist coding for the inverter that would not be available for suppliers. Ron also ran a full diagnostic to insure that all was in good working order afterwards. Without Rons support and patient assistance I doubt I would ever have got the system back up and running. Well done and thankyou and you have a customer for the future.

Philip Davey · Jun 2026 Google

STS were incredibly responsive and helpful In diagnosing an issue with my GivEnergy inverter. Although distance meant it was impractical for me to use them to fully solve the issue, I’m grateful for the help and detail they provided. Don is a real professional gent and a hero in my eyes.

Adam Miller · Jun 2026 Google

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.

M Foster · Jul 2026 Google

What a fantastic service. Had my fault diagnosed within minutes and actually managed to resolve the issue remotely within a few minutes more. This guy is like a “Solar Batman” helping consumers fix their problems using his extensive industry knowledge and expertise. Outstanding service. Thank you so much.

Andrew Palmer · May 2026

customer · Apr 2026

Philip Davey · Jun 2026 Google

M Foster · Jul 2026 Google

Chemistry & BMS

Lithium chemistry and the Battery Management System

Two chemical formulations dominate the UK solar market. Understanding the difference helps you choose the right battery and understand its behaviour.

LFP: Lithium Iron Phosphate (now standard for UK domestic)

LFP uses an iron phosphate cathode. This chemistry is thermally stable — harder to trigger thermal runaway (fire) even if the pack is physically damaged or over-charged. LFP batteries last 8,000–10,000 full-depth cycles (100% charge to 0% discharge). Performance in cold weather (5°C +) is excellent. Most UK residential systems today use LFP (GivEnergy, Growatt, Sunsynk, Solis all standard LFP packs).

Why LFP is preferred: Safety, long cycle life, cold weather performance, and warranty depth (10 years typical).

NMC: Nickel-Manganese-Cobalt (older, fewer new installations)

NMC has a nickel-based cathode. Higher energy density (lighter per kWh) but shorter cycle life: 3,000–5,000 cycles. More prone to thermal runaway if damaged. Cold weather performance weaker. NMC is being phased out in residential solar — you are more likely to encounter it in legacy systems (pre-2023). Not recommended for new installations in the UK.

The Battery Management System (BMS): your battery's safety brain

The BMS is an electronic system embedded in or mounted next to the battery pack. Its job is to monitor and protect:

•Cell voltage: prevents individual cells from overcharging (>4.2V) or over-discharging (<2.5V)

•Temperature: cuts power if cells exceed safe range (typically 60°C max)

•Current limiting: prevents charge/discharge at rates that would damage cells

•Fault detection: internal short circuit, water ingress, or BMS failure triggers immediate disconnect

The inverter continuously communicates with the BMS. If the BMS reports a fault, the inverter immediately stops charging or discharging. This is why you sometimes see a battery error code but the battery still has charge — the BMS has isolated the pack for safety.

SoC & DoD

State of Charge (SoC) and Depth of Discharge (DoD)

SoC is what your app shows you. DoD is how much of that you actually use each day. Understanding both explains why manufacturers limit your 80% and why this helps your battery last longer.

State of Charge (SoC) is the battery's current energy level (0–100%)

SoC is shown in your app as a percentage. 100% SoC means the battery is full. 0% SoC means it is empty. The BMS measures this by integrating current flow over time and comparing cell voltages. You cannot have negative SoC — the BMS stops discharge well before the battery is completely empty (typically at 5–10% to protect the cells).

Why systems often cap charge at 80% SoC upper limit

Lithium cells experience stress at high voltage. Charging to 100% every cycle ages the cells faster. By capping at 80%, the system trades 20% capacity availability for measurably extended lifespan — studies show you can add 5+ years to battery life. The last 20% of charge is expensive in terms of cell degradation.

You can reconfigure most systems to charge to 90% or 100% if you need the extra capacity — your installer or engineer can adjust this. But be aware the battery will age faster.

Depth of Discharge (DoD) is how much of the battery's capacity you use each day

If your 10 kWh battery charges to 80% (8 kWh usable) and you discharge 5 kWh per day, your DoD is 62.5%. Shallow DoD cycles extend battery life dramatically:

• 30% DoD cycles: 15,000–20,000 cycles (20+ years)

• 50% DoD cycles: 10,000–12,000 cycles (15+ years)

• 100% DoD cycles: 8,000–10,000 cycles (10+ years)

If your daily energy use only requires 30% DoD, the battery will outlast the inverter. Most UK residential systems achieve 40–60% DoD on average, which is ideal.

Coupling Architecture

AC coupling vs DC coupling: efficiency and retrofit

The two ways to connect a battery to solar. Each has different efficiency, retrofit implications, and failure modes.

DC coupling: battery on the same DC bus as the solar panels

In a DC-coupled system, the solar array, battery, and single inverter share the same DC bus. Solar DC current charges the battery directly, bypassing an AC-to-DC conversion stage. This is the architecture of most new hybrid inverters (GivEnergy, Growatt SPA series, Sunsynk Turbo-X, Solis RHI).

✓Efficiency: 98–99% round-trip (fewest conversion steps)

✓Simplicity: one inverter, one DC bus, single point of control

✓Cost: lower hardware cost than AC-coupled

•Limitation: battery cannot be retrofitted to existing solar easily (requires replacing the original inverter)

AC coupling: battery has its own inverter connected to household AC

In AC-coupled retrofit systems, the existing solar inverter feeds AC into the house. A separate battery inverter connects to the AC circuit (usually before the consumer unit or via a dedicated circuit) and charges/discharges bidirectionally. The two inverters operate independently but coordinate via communication protocols.

✓Retrofit-friendly: can add battery to 10-year-old solar without replacing existing inverter

✓Flexibility: battery size can be chosen independently of solar capacity

•Efficiency: 92–96% round-trip (two AC-to-DC and DC-to-AC conversions)

•Complexity: two inverters, separate protection, coordination required

•Cost: higher hardware and installation cost

Efficiency

Round-trip efficiency: not all stored energy returns

Energy is lost as heat during charge and discharge. Round-trip efficiency tells you what percentage actually comes back out. This matters for financial modelling.

Measuring round-trip efficiency

Round-trip efficiency = (Energy discharged / Energy charged) × 100%. If you charge the battery with 10 kWh and only 9.5 kWh comes back out, round-trip efficiency is 95%. The 0.5 kWh loss is dissipated as heat in the inverter, battery, and wiring.

Typical values:

• DC-coupled: 94–98%

• AC-coupled: 92–96%

Where efficiency losses occur

Three sources of loss during charge-discharge cycle:

1.Inverter inefficiency: DC-AC and AC-DC conversion is typically 95–98% efficient each direction

2.Battery internal resistance: lithium cells have internal resistance (~10 mΩ per cell) that dissipates heat during current flow

3.Parasitic draw: the BMS consumes power continuously to monitor cells, even when battery is idle

Using efficiency in financial modelling

If your business case assumes you store 10 kWh daily and use all of it, but round-trip is 95%, you only actually have 9.5 kWh available. Your payback period will be 5% longer. Account for efficiency when calculating ROI. Monitoring portals sometimes show efficiency figures — check the battery health section or ask your installer what the system's round-trip efficiency is (most will know within 0.5%).

Degradation

Battery degradation: what to expect over 10+ years

Lithium batteries age chemically with every charge cycle and also with calendar time. Understanding degradation helps you plan for replacement and avoid panic when your battery's max SoC drops slightly.

Cycle-based degradation: every charge/discharge ages the battery

LFP batteries typically lose 0.5–1% capacity per 100 full-depth cycles. If you cycle 300 times per year:

After 3 years: ~10 capacity loss (3 × 300 × 1% = 9%)

After 10 years: ~30% capacity loss (10 × 300 × 1% = 30%)

At 10 years: battery retains ~70% of original capacity

However, shallow cycles (30% DoD) age batteries slower. If you only cycle 30–50% DoD, you can reduce degradation to 0.1–0.3% per 100 cycles, extending usable life to 15+ years.

Calendar aging: batteries age even if not used

Lithium cells age chemically over time regardless of use. A battery sitting at 50% SoC in a 25°C room will lose ~2–3% capacity per year just from calendar aging. Hot environments accelerate this (5% per year at 35°C). This is why batteries stored long-term should be kept cool and at 30–50% SoC.

What you will notice as the battery ages

Degradation manifests gradually:

•Year 1–3: minimal change, battery health shown as 95–100%

•Year 5: battery health ~90%, max SoC might drop 1–2%

•Year 10: battery health ~70–80%, you have 20–30% less usable energy than day one

The inverter portal shows battery health as a percentage. Check it quarterly to track degradation rate. If health drops faster than expected (5%+ in one year), investigate: high temperatures, deep cycles, or BMS fault.

Manufacturer warranties typically cover 10 years or 70% capacity retention

Most manufacturers (GivEnergy, Growatt, Sunsynk, Solis) warrant the battery for 10 years or until capacity drops to 70%, whichever comes first. If your battery fails or degrades rapidly before 70%, warranty repair/replacement is available. Degradation to 70% over 10 years is normal wear and not typically covered.

Frequently asked questions

Can I increase the SoC upper limit to 100% to get more usable capacity?

Yes, most systems can be reconfigured to charge to 90% or 100%. The trade-off is accelerated degradation — charging to 100% every cycle ages the battery 30–40% faster. Most installers default to 80% because the extended lifespan is worth the 20% capacity reduction. For seasonal use (winter when solar is limited), you can temporarily increase to 90% or 100% then drop back to 80% in summer. Check with your installer whether your system supports this flexibility.

Is my battery safe if it shows high temperature warnings?

The BMS will automatically disconnect the battery if internal temperature exceeds ~60°C to protect the cells. Temperatures above 60°C dramatically accelerate chemical degradation and increase thermal runaway risk. If you see temperature warnings in your portal, investigate: is the battery in direct sunlight? Is ventilation blocked? Is the room temperature consistently very high? These are correctable installation issues. Contact your installer to consider relocating the battery if necessary.

What happens if I fully drain the battery every day?

100% DoD cycles daily will degrade the battery significantly faster — expect 30–50% capacity loss within 5–7 years instead of 10+. The BMS will cut off discharge around 5–10% SoC to prevent over-discharge damage, so you can't truly reach 0%. If your load genuinely requires deep cycles, you can configure the system to allow it — just accept the shorter battery life. Most UK domestic users don't need deep cycles: daytime solar generation typically meets the load, and overnight use is moderate.

Should I be concerned if battery health drops 5% in the first year?

A 3–5% drop in year one is normal — lithium batteries experience burn-in degradation in months 1–6 as cell chemistry stabilises. After that, degradation should settle to roughly 0.5–1% per 100 cycles. If health continues dropping rapidly after year one (5%+ per year), investigate: the battery may be cycling at unusually high depth, running too hot, or the BMS may be misreporting capacity. A remote health check will identify which.

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