The cheaper battery is the expensive one
Lead-acid wins on the day you buy it and loses by year six. That is the entire argument, and it is worth seeing laid out properly before you choose — because a bank cannot be half upgraded later.
| Lead-acidThe cheaper purchase | LithiumThe cheaper decade | |
|---|---|---|
| Up-front cost | Lower | Two to three times higher |
| Usable capacity | About half the rating | Most of the rating |
| Typical life here | 3–5 years | 8–15 years |
| Maintenance | Checking, topping up, ventilation | Essentially none |
| Space needed | More, plus ventilated housing | Less |
| Deep discharge | Damages it | Tolerated by design |
| Charge speed | Slower | Faster |
| Cost across ten years | Higher, once replacements are counted | Lower |
The same money over ten years
Illustrative, using a bank sized to run lights, fans, a fridge and electronics through a typical evening outage. Your figures will differ; the shape of the comparison will not.
Lead-acid
- Year 0Bank purchasedPKR 220,000
- Year 4Bank replacedPKR 220,000
- Year 8Bank replaced againPKR 220,000
- Year 10Ageing, third replacement due—
Ten-year totalPKR 660,000
Plus periodic maintenance and a ventilated space.
Lithium
- Year 0Bank purchasedPKR 520,000
- Year 4Still working—
- Year 8Still working—
- Year 10Well within expected life—
Ten-year totalPKR 520,000
No maintenance, less space, more usable capacity throughout.
Choosing what stays on
Bank size follows this list, not the other way round. Putting the whole house on backup is what drains a bank in an hour and makes people think they were sold the wrong battery.
We go through this with you at the survey, circuit by circuit, before anything is quoted.
- LightsUsually on
- Ceiling fansUsually on
- RefrigeratorUsually on
- Router and TVUsually on
- Phone chargingUsually on
- Water pumpUsually off
- Air conditioningUsually off
- Electric geyserUsually off
Battery questions
- Is lithium worth the extra over lead-acid?
- Across ten years, yes, for most households. Lithium costs two to three times more up front and lasts two to three times longer, with roughly double the usable capacity from the same rated size. Lead-acid is the cheaper purchase and the more expensive decade.
- Can I replace just one battery in my bank?
- No. A series bank runs at the level of its weakest battery, so a new unit among tired ones is dragged down and its life wasted. Banks are replaced together, which is why it pays to buy the right chemistry the first time.
- How big a battery bank do I need?
- Add up what must keep running, multiply by the hours you need it for, then double it for lead-acid because you should not discharge below half. Lights, fans and a fridge is a modest bank. Add air conditioning and the number changes sharply.