Battery Sizing
How to Size Your Battery Bank
Determine the right battery capacity for brownout backup in your Philippine home.
8 min read
Simple and practical
Beginner level
No solar background needed
PH context
Made for local homes
What you will understand
Visual Learning Map
Lesson Guide
Battery Sizing Formula
Step 1: List critical loads (what you need during brownouts) Step 2: Calculate total watts Step 3: Multiply by backup hours needed Step 4: Divide by depth of discharge
Battery kWh = (Load Watts × Backup Hours) ÷ 1000 ÷ DoD
PH Example: Essential Backup
| Appliance | Watts | Hours |
|---|---|---|
| LED lights (5) | 50W | 6h |
| Fans (2) | 150W | 6h |
| Router | 15W | 6h |
| Refrigerator | 150W | 6h |
| Total | 365W |
For 6-hour backup: 365 × 6 ÷ 1000 ÷ 0.8 = 2.7 kWh battery
For aircon backup, you'd need 10+ kWh — much more expensive.
Frequently Asked Questions
How many backup hours should I plan?
4–8 hours for typical brownouts. 12–24 hours for typhoon-prone areas.
What is DoD?
Depth of Discharge — the percentage of battery capacity you can safely use. LiFePO4: 80–90%.
12V or 48V battery bank?
48V is standard for home solar. 12V is for small RV/cabin setups only.
One big battery or multiple?
Matched sets in parallel are fine. Don't mix different brands/ages.
Does solar recharge the battery daily?
Yes — hybrid inverters prioritize solar charging. Full recharge depends on panel size and sun.
Common Mistakes to Avoid
Sizing for full home including aircon
Aircon on battery is expensive. Size for critical loads, use generator for extended aircon needs.
Forgetting inverter conversion losses
Add 10–15% to battery size to account for DC-AC conversion losses.
No low-voltage protection
Deep discharge kills batteries. Ensure your inverter has adjustable low-voltage cutoff.