How to Size a Battery Bank for Load-Shedding Backup in Lahore
Size a load-shedding battery bank in four steps: add up the watts you will run on backup, decide how many hours you need, calculate the energy (watts × hours), and size the battery so a normal outage only drains it to about half. For most Lahore homes running fans, lights and a TV for 3–4 hours, that is a 24V pair of ~185 Ah tubular batteries.
Quick summary
- Step 1: list backup load in watts. Step 2: hours needed. Step 3: watt-hours = W × h.
- Step 4: size so a normal outage drains the bank only to ~50% — that is what makes it last.
- Usable energy ≈ battery voltage × Ah × 0.5 × 0.85 (inverter losses).
- Typical Lahore home (fans + lights + TV, 3–4 h): 24V × two ~185 Ah tubular.
- We size it free — send your inverter and load: 0309-7179133.
Step 1: list what you will run on backup
Be realistic — the more you back up, the bigger and more expensive the bank. A sensible essential-load list for load-shedding:
| Item | Rough watts each | Example count |
|---|---|---|
| Ceiling fan | 75 W | 5 = 375 W |
| LED light | 12 W | 10 = 120 W |
| LED TV | 60 W | 1 = 60 W |
| Router + ONT | 20 W | 1 = 20 W |
| Phone / laptop charging | 45 W | 1 = 45 W |
| Total | ≈ 620 W |
Adding a refrigerator adds roughly 150–250 W average (it cycles on and off). An inverter AC adds 800–1,500 W and changes the maths completely — treat that as a separate, larger project.
Step 2: decide the hours
Match this to your area's actual load-shedding. If outages run 2 hours at a time, sizing for 3–4 hours gives a comfortable margin. Sizing for 8 hours “just in case” buys a much bigger, costlier bank you rarely use fully.
Step 3: calculate the energy
Energy needed = load × hours. For the 620 W example over 3 hours: 620 × 3 = 1,860 watt-hours (Wh).
Step 4: size the battery (the important bit)
You cannot use all of a lead-acid battery — draining it below ~50% every day destroys it quickly. And the inverter loses some energy in conversion. So:
Usable energy ≈ battery voltage × Ah × 0.5 × 0.85
- One 12V, 185 Ah tubular: 12 × 185 × 0.5 × 0.85 ≈ 944 Wh usable.
- A 24V pair of 185 Ah: about 1,890 Wh usable.
- A 24V pair of 200 Ah: about 2,040 Wh usable.
So the 1,860 Wh example needs roughly a 24V pair of 185–200 Ah tubular batteries. If your inverter is 12V, a single large battery gives less runtime for the same load.
Match the count to the inverter
- 12V inverter → 1 battery. 24V → 2 in series. 48V → 4 in series.
- Want more hours later? Add another identical series set in parallel — matched batteries only, never old with new.
Why “drain to 50%” matters so much
A bank sized so a normal outage takes it down to 50% can last 4–6 years. The same batteries flattened to the inverter cut-off every day often fail inside two. Sizing generously up front is cheaper than replacing an under-sized bank early.
Let us do the sums
Send your inverter make, VA and DC voltage, your backup load (or just a list of what you want to run), and your hours. We will give you the exact Ah, battery type and count, quote today's price after old-battery exchange, and install and configure it across Lahore.
Size your load-shedding battery bank
Send your inverter, backup load and hours needed — we will give you the exact Ah, type and count, installed in Lahore.
WhatsApp 0309-7179133 Call nowFrequently asked questions
How do I work out what size battery bank I need?
Add up the watts you will run on backup, multiply by the hours you need to get watt-hours, then size the battery so a normal outage only drains it to about 50%. Usable energy is roughly battery voltage x Ah x 0.5 x 0.85.
What size bank runs fans, lights and a TV for 3-4 hours?
For a typical load around 600 W, roughly a 24V pair of 185–200 Ah tubular batteries. If your inverter is 12V, a single large battery gives less runtime for the same load.
Why size for only 50% discharge?
Draining a lead-acid battery below about 50% every day destroys it within a couple of years. A bank sized so a normal outage only takes it to 50% can last 4–6 years, so sizing generously up front is cheaper overall.
Can I run an AC on a load-shedding battery bank?
Only with a much larger bank and a suitable inverter — an inverter AC adds 800–1,500 W and changes the sizing completely. Most load-shedding banks are sized for fans, lights, TV, routers and chargers.
How do I add more backup hours later?
Add another identical series set of batteries in parallel — for example, go from two to four on a 24V inverter. Always use matched batteries of the same age, type and Ah; never mix old and new.