Solar Storage Battery: Solar Batteries for Off-Grid & Backup

A solar storage battery stores photovoltaic energy for use when the sun is not shining. Solar duty is the hardest working cycle in lead-acid service: a daily charge-discharge cycle, often to 50% or deeper, in locations where the ambient temperature may exceed 40 °C. The battery that survives this is a deep cycle design — not a starting battery.

Chengguang supplies solar storage through two channels: its heavy-duty flooded models for cost-driven cyclic duty, and sealed AGM/GEL batteries manufactured to order for off-grid and backup installations.

Key Takeaways

• Core rule — Solar duty = daily deep cycling to 50%+ DoD — requires deep-cycle, not starting, batteries.
• Options — Flooded (cost-driven), AGM (sealed), GEL (longest cycle life) — all need the correct charge-controller voltage.
• Chengguang — 145G51/190H52 suit cyclic duty (80% DoD tested); AGM/GEL solar banks made to order.
• Sizing example — 1,000 Wh/day → 391 Ah at 50% DoD with 2 autonomy days.

What Solar Duty Demands

Solar Battery Options

Capacity vs Discharge Rate (Peukert)

A battery’s usable Ah shrinks as discharge current rises. A 100 Ah (C20) unit is rated at a 5 A draw over 20 hours; at heavier loads it delivers less:

Size the bank for the highest sustained load, not the daily average. A 1,000 W inverter at 12 V pulls ~83 A (plus inverter losses) — at that rate a 200 Ah bank delivers closer to 130–150 Ah before voltage sags.

The Chengguang Solar Range

Chengguang’s catalog heavy-duty models are the flooded option for cyclic duty; AGM/GEL are produced to order for sealed solar installations.

Sizing a Solar Battery Bank

1. Calculate daily load in watt-hours (Wh) and convert to Ah at system voltage (Wh ÷ V = Ah).
2. Set the DoD budget. Bank Ah required = daily Ah ÷ allowable DoD ÷ 0.85 (round-trip efficiency).
3. Add autonomy days for cloudy periods: multiply by the number of days the system must run without sun.
4. Match the charge controller. Set absorb/float voltages to the battery chemistry — 14.4–14.8 V absorb for AGM, lower float for GEL. An incorrect setpoint is the leading cause of early solar battery failure.

Example sizing: a 1,000 Wh/day cabin load at 12 V = 83 Ah/day. At 50% DoD with 2 autonomy days: 83 ÷ 0.5 ÷ 0.85 × 2 = 391 Ah — roughly a 2 × 190H52 (200 Ah each) parallel bank, or a matched AGM/GEL bank to order.

Series / Parallel Configuration

All batteries in a string must be the same model, age, and capacity. Mismatched strings develop unequal state-of-charge — one battery overcharges and gasses while another starves and sulfates.

Buying Considerations

1. Deep cycle, not starting. A starting battery in a solar array will fail in months.
2. Series/parallel strings must use identical batteries of the same age and capacity.
3. Temperature derating. At 40 °C, derate service life and check the battery’s temperature rating before specifying.
4. Sealed for inaccessible installs. If the bank is in a sealed box or indoors, AGM/GEL avoids hydrogen venting and watering.

Charge Controller Matching

The charge controller — MPPT or PWM — is what keeps a solar battery alive. The single most common cause of early solar-battery death is an absorb/float voltage set for the wrong chemistry:

Set the controller to the battery’s chemistry, not the panel’s output. MPPT controllers extract more energy in partial light; PWM is cheaper and adequate for small systems — but both must have the correct voltage setpoints.

Temperature Derating

Lead-acid chemistry is temperature-sensitive, and solar banks often live in hot, exposed locations:

• Above 25 °C, capacity rises slightly but service life falls — every 8–10 °C roughly halves VRLA design life.
• At 40 °C ambient, derate expected service life and verify the battery’s temperature rating before specifying.
• Below 0 °C, available capacity drops sharply, and a discharged flooded bank can freeze.

A temperature-compensated charge controller (with a battery temp sensor) automatically adjusts voltage setpoints and is worth the small premium for any permanently installed off-grid bank.

Temperature Compensation Coefficients

Charge voltage must be lowered as temperature rises. The standard correction is approximately −3 mV/°C per cell for flooded and −4 mV/°C per cell for AGM/GEL, referenced to 25 °C (2.40 V/cell absorb):

A fixed 14.40 V absorb on a 45 °C bank overcharges it by ~0.36 V — enough to gas a GEL bank dry within months. A temperature sensor (or a manual seasonal adjustment) is the fix.

Autonomy Days & DoD Budget

Two variables dominate solar-bank sizing — and they trade off against each other:

A 50% DoD budget with 2–3 autonomy days is the standard off-grid starting point; it roughly doubles cycle life versus an 80% budget while still covering cloudy stretches. For a 1,000 Wh/day cabin: 83 Ah/day ÷ 0.5 ÷ 0.85 = 196 Ah × 2 days = 391 Ah.

Panel-to-Battery Balance (Worked Example)

A battery is only as healthy as the charge it receives. For the 1,000 Wh/day cabin above, the array must replace roughly 1,000 ÷ 0.8 ≈ 1,250 Wh/day once controller, wiring, and round-trip losses are counted. At 4.5 peak-sun hours that is 1,250 ÷ 4.5 ≈ 280 W of panel; add a 20% margin for cloud and panel aging → a ~330 W array. An undersized array or controller leaves the bank chronically undercharged — the single most common cause of early sulfation and capacity loss off-grid.

Depth of Discharge vs Cycle Life

The deeper the daily discharge, the fewer cycles a lead-acid bank delivers — this trade-off drives solar sizing:

Halving the DoD budget (80% → 50%) roughly doubles cycle life — which is why the 50%-DoD starting point is standard off-grid practice, and why an undersized bank costs more in the long run than a larger one.

Placement, Venting & Safety

• Vent flooded banks — off-gassing hydrogen must vent to open air, never into a sealed room.
• Sealed (AGM/GEL) for enclosed installs — no watering, minimal gassing, safe in cabins and RVs.
• Temperature — keep the bank out of direct sun; heat is the fastest way to shorten lead-acid life.
• Fusing — every string needs over-current protection sized to the cable, not the load.

Off-Grid vs Backup (Hybrid) Solar

Two solar use cases put different demands on the battery:

An off-grid bank needs deep-cycle construction and a DoD budget; a backup bank spends most of its life at float and only cycles during outages, so VRLA (AGM/GEL) float life matters more than cycle count. Sizing is the same formula either way — the difference is which battery attribute you optimize.

Preguntas frecuentes

How many batteries do I need for off-grid solar? Size by daily load: required Ah = daily Ah ÷ allowable DoD ÷ 0.85, then multiply by autonomy days for cloudy periods.

Flooded or AGM for solar? Flooded for cost-driven, accessible installs; AGM/GEL for sealed or inaccessible banks. Both require a charge controller set to the correct chemistry voltage.

How long does a solar battery last? 5–10+ years for a properly sized and maintained deep-cycle bank; an undersized bank cycled past 80% DoD fails much sooner.

Do I need a special charge controller? Any controller works if its absorb/float voltages match the battery chemistry — but a temperature-compensated MPPT controller is worth the premium for permanent off-grid installs.

Can I mix old and new batteries in a bank? No — all batteries in a string must be the same model, age, and capacity, or the bank develops unequal state-of-charge and fails early.

Related Articles

• Deep Cycle Battery Guide
• UPS Battery Guide
• AGM Battery Guide
• 190H52 Battery
• 145G51 Battery
• C20 Capacity — Complete Guide
• VRLA Battery Technology Reference
• Request Solar OEM Quote

Sources & Verification

Specifications on this page are sourced from Chengguang Power Tech factory technical documentation and tested to JIS D 5301, DIN EN 50342-1, SAE J537, and IEC 60095-1. Contact Chengguang for the exact data sheet. Every batch ships with a Certificate of Analysis (CoA).

Author: Chengguang Engineering Team · Reviewed: IATF 16949 Quality Department · Last updated: 2026-08-19