Off-Grid Solar Calculators

Battery storage

Lead-Acid to LiFePO4 Upgrade Calculator

Lead-acid and LiFePO4 amp-hour ratings are not interchangeable. A 100 Ah lithium pack used to 95% DoD holds about the same usable energy as a 200 Ah lead-acid bank used to 50%. This tool matches usable watt-hours and estimates pack mass.

Inputs

Ah

Rated amp-hours of the existing flooded, gel or AGM bank.

System voltage of the battery or series string.

How deep you actually use the lead-acid bank. 50% is the usual cycle-life limit.

Most LiFePO4 house batteries can be used near 95% of rated capacity.

Results

Usable energy to match
1,200Wh

Energy you actually take from the lead-acid bank.

LiFePO4 capacity needed
105Ah

Rated amp-hours at the same nominal voltage.

Lead-acid mass (typical)
60.0kg
LiFePO4 mass (typical)
11.6kg
Weight saved
48.4kg

Recommended gear

Engineering methodology

Match usable energy, not nameplate amp-hours: Ah_LFP = Ah_lead × DoD_lead ÷ DoD_LFP. Usable watt-hours = Ah_lead × V × DoD_lead (Wh = Ah × V). Mass uses typical 12 V pack densities of about 0.30 kg/Ah for lead-acid and 0.11 kg/Ah for LiFePO4, scaled with voltage. Those densities are planning averages, not a shipping spec.

Frequently asked questions

Does a 100 Ah LiFePO4 battery replace a 200 Ah lead-acid bank?

Often, for usable energy: 200 Ah lead-acid at 50% DoD is 100 Ah usable; 100 Ah LiFePO4 at 95% DoD is about 95 Ah usable. Confirm BMS continuous current, charge voltage and physical fit before swapping chemistries.

Why can’t I compare lead-acid and lithium amp-hours one-for-one?

Nameplate Ah is capacity to the manufacturer’s cutoff. Lead-acid cycle life collapses if you regularly use most of that. LiFePO4 can typically use about 95%. Equal Ah labels therefore do not mean equal usable watt-hours.

Are the weight numbers exact for my batteries?

No. They scale typical 12 V kg-per-Ah figures. Case, cells, BMS and voltage change mass. Use the manufacturer’s weight for installation and vehicle payload.

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