Lead-acid against LiFePO4: usable capacity, voltage and life
Two 100 Ah batteries on the same 10 A load. The lead-acid is at 12.0 V and half empty after five hours, where it should stop; the LiFePO4 holds 13 V and goes on for eight. Peukert takes more from the lead-acid at high current, and every hour it spends below half charge costs it capacity. Lead-acid still wins on price and on standby duty; this lesson shows the price of that price.
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How it works
Lead-acid: 100 % at 0.00 V, Peukert factor ×1.00 at 10 A (C/10). LiFePO4: 100 % at 0.00 V. Usable: about 50 Ah against 80–90 Ah from the same nameplate, which is why a lead-acid bank is sized at twice the Ah.
Open the lead-acid's datasheet card for the full comparison, including where it still makes sense.
Try it on the bench
- Run at this speed: the lead-acid reaches 50 % in about five hours of battery time; stop there in real life.
- Raise both loads to 30 A: Peukert makes the lead-acid lose capacity faster than the current alone explains.
- Select the lead-acid and set it to AGM or gel: a different gassing voltage, which the charge controller must respect.
Parts on the bench
- Lead-acid battery
- 2 × Electronic load
- 2 × Digital multimeter
- LiFePO4 battery
In the course
Solar PV Systems, module “7 · Batteries and charging”.
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