Ask a buyer what limits a solar street light’s life and most will say the LED. In practice, the LED is usually the last component to fail. The battery decides when the project starts costing money again.

Why Chemistry Matters

Older lithium chemistries and lead-acid packs lose capacity faster in heat. LiFePO4 is more thermally stable, which is why it has become the default for outdoor solar in hot markets. But “LiFePO4" on a datasheet is the beginning of the question, not the answer.

The Number Buyers Should Ask For

Cycle life at operating temperature. A pack rated at 6,000 cycles is meaningful only if the test condition resembles the site. At 25°C in a laboratory, almost any lithium pack looks good. At 45°C with a daily deep discharge, the differences appear within two years.

Ask three questions: what is the cycle life at 45°C, what depth of discharge was used, and what is the capacity retention after 2,000 cycles? A supplier who can answer all three is selling engineering, not adjectives.

Thermal Design Around the Pack

• Shade the compartment. Mounting so the panel overhangs the battery bay reduces peak temperature.
• Separate the driver. Electronics and cells should not share the hottest zone.
• Allow ventilation without ingress. A breathable membrane equalises pressure without letting water in.
• Charge conservatively when hot. A controller that reduces charge current at high temperature extends life.

Why Cheap Packs Fail First

Low-cost packs often use lower-grade cells, thinner tabs and minimal balancing. They pass an initial capacity test and fail after a year of daily cycling. The buyer sees a lamp that dims earlier each month and assumes the LED is degrading, when the pack is the problem.

“The LED has a ten-year story. The battery has a three-year invoice." — Distributor, Nigeria

What to Put in the Specification

1. Chemistry: LiFePO4, stated explicitly.
2. Cycle life at 45°C with depth of discharge stated.
3. Charging temperature limits and cut-off behaviour.
4. Replaceability: module-level access without removing the head.
5. Warranty terms that cover capacity retention, not just failure to start.

Battery chemistry is not a detail for the engineering annex. It is the line item that determines whether the project is still lit in year five.