For most of the continental United States, this means angles between 25-45 degrees. You can fine-tune this by subtracting 10-15 degrees for summer optimization or adding 10-15 degrees for winter optimization.
Temperature is the ultimate battery killer: For every 8°C (14°F) increase above 25°C, battery life can be reduced by up to 50%. Indoor installation in climate-controlled spaces can extend lifespan by 3-5 years compared to outdoor installations in hot climates.