A few years ago, a bank of four deep-cycle lead-acid batteries was the standard load shedding fix. They were cheap, every auto spares shop sold them, and any electrician could wire them up. Plenty of those banks are now sitting dead in garages.
Lithium iron phosphate (LFP) batteries cost more up front. They also last far longer and give you more of what you paid for. The way to compare them is cost per kWh delivered over the battery’s life, not price on the day.
What you can actually use
Lead-acid batteries hate being drained. Take them below about half charge regularly and their life drops sharply, so a sensible system only uses 50% of the rated capacity.
LFP is far more forgiving. Most are set to use 80% to 95% of their capacity every day without complaint.
So a lead-acid bank rated at 9.6 kWh gives you about 4.8 kWh. A single 5.12 kWh LFP battery gives you about 4.6 kWh. Roughly the same usable energy, from a battery half the nominal size.
How many times it can do that
This is where the gap opens up.
| Lead-acid (AGM or gel) | LFP | |
|---|---|---|
| Usable depth | 50% | 80% to 95% |
| Typical cycle life | 300 to 1,200 | 4,000 to 6,000+ |
| Typical lifespan in daily use | 2 to 5 years | 10 years or more |
| Weight for 5 kWh usable | Around 250 kg | Around 50 kg |
| Maintenance | Check terminals, keep cool | None to speak of |
Cycle figures vary a lot by brand and by how hot the battery runs, so treat the table as a range, not a promise. Check the warranty, which usually states both years and cycles.
The sum that settles it
Multiply usable capacity by cycle life and you get the total energy the battery will deliver before it’s worn out.
| Usable per cycle | Cycles | Lifetime energy | |
|---|---|---|---|
| Lead-acid bank (9.6 kWh rated) | 4.8 kWh | 600 | 2,880 kWh |
| LFP battery (5.12 kWh rated) | 4.6 kWh | 6,000 | 27,600 kWh |
That’s nearly ten times the energy from the lithium battery. Even if it costs twice or three times as much as the lead-acid bank, each kWh it delivers is much cheaper.
When lead-acid still makes sense
If the battery will only ever see occasional outages, a few cycles a month, lead-acid’s short cycle life matters less. Its calendar life still runs out, but you won’t burn through 600 cycles. A small backup for a gate motor or alarm is a reasonable use.
For anything that cycles every day, which is any battery paired with solar, LFP wins on cost as well as convenience.
Two things to check before you buy
First, make sure the battery talks to your inverter. Most LFP batteries connect to the inverter over a communication cable so the two agree on charge limits. A battery that isn’t on your inverter’s compatibility list may still work, but it’ll work worse.
Second, look for a real local warranty with a real local agent. A ten-year warranty from a company with no South African presence is a ten-year promise you can’t collect on.
