Usable capacity is not rated capacity
A tubular lead-acid bank is normally limited to roughly half its rated capacity if you want reasonable life. An LFP lithium pack routinely delivers eighty to ninety percent of its rating. So a 10 kWh lithium pack and a 10 kWh lead-acid bank are simply not the same purchase.
Heat is the deciding factor in Karachi
Battery life is temperature-sensitive, and Karachi utility rooms sit warm for eight months of the year. Lead-acid loses life quickly above 30°C and needs ventilation and water top-ups. LFP tolerates heat better, is sealed, and reports its own state of health through the BMS.
Cost per usable cycle
Compare on cost per usable kWh over the expected cycle count, not on sticker price. Once you divide the price by usable capacity and by realistic cycles, lithium usually lands cheaper across the life of the system, while also freeing floor space and eliminating maintenance visits.
- Lithium LFP — higher upfront, sealed, BMS-protected, deep discharge, long cycle life
- Tubular lead-acid — lower upfront, shallow usable depth, ventilation and watering required, shorter life in heat
Sizing around critical loads
Do not size a battery to your whole house. List what must stay alive during an outage — fridge, fans, lights, router, water pump — and size the pack to run that list for the outage duration you actually experience in your neighbourhood.
Frequently asked questions
- Can I add a lithium battery to an existing solar system?
- Only if your inverter is hybrid or battery-ready with a compatible communication protocol. On a pure on-grid inverter you need an AC-coupled solution or an inverter change.