Battery Deal Check Calculator
What does a battery or power station offer really cost? Enter the price you see, the capacity, the chemistry and the rated cycles from the data sheet. The calculator shows the price per usable kWh and the cost per kWh stored over the battery life, for up to three offers side by side.
Offer A
The price you see in the shop, in any currency. Results are in the same currency.
Used to turn Ah into Wh: 12.8 V for a 12 V LiFePO4, 12 V for lead batteries.
Planning default: 80 %
Planning default: 3500 cycles
Enter the cycle count from the data sheet, at the depth of discharge set above.
Remaining capacity after the rated cycles, usually 70 or 80 %. Leave empty to ignore capacity fade.
Enter a price, a capacity, a depth of discharge and a cycle count to see the result.
Offer B
The price you see in the shop, in any currency. Results are in the same currency.
Used to turn Ah into Wh: 12.8 V for a 12 V LiFePO4, 12 V for lead batteries.
Planning default: 50 %
Planning default: 600 cycles
Enter the cycle count from the data sheet, at the depth of discharge set above.
Remaining capacity after the rated cycles, usually 70 or 80 %. Leave empty to ignore capacity fade.
Enter a price, a capacity, a depth of discharge and a cycle count to see the result.
Plan the whole system around the battery
VoltPlan designs full electrical systems for campers, boats, and off-grid setups with automatic wire sizing, fuse placement, and battery configurations.
Design Your SystemHow the calculator works
The price is always your own input, in any currency. VoltPlan does not know or show shop prices. The calculation is a simple model with four steps:
- Nameplate energy: Wh = Ah × nominal voltage (12.8 V for LiFePO4, 12 V for lead batteries). If the offer states Wh, that value is used directly.
- Usable energy: usable kWh = Wh × usable depth of discharge ÷ 1000.
- Price per usable kWh: price ÷ usable kWh. This is what one full usable charge costs you up front.
- Cost per stored kWh: price ÷ (usable kWh × rated cycles × average capacity). With an end-of-life capacity, the model assumes the capacity fades linearly from 100 % to that value, so the average capacity is (1 + end-of-life capacity) ÷ 2, for example 0.9 at 80 %. Without it, the average capacity is 1.
Planning defaults per chemistry
When you pick a chemistry, the calculator fills in these values. They are rough planning assumptions shared by all VoltPlan battery calculators, not manufacturer figures. Replace them with the values from the data sheet of the offer you are checking. The default end-of-life capacity is 80 %.
| Chemistry | Nominal voltage | Usable depth of discharge | Cycles (planning value) |
|---|---|---|---|
| LiFePO4 | 12.8 V | 80 % | 3,500 |
| AGM | 12 V | 50 % | 600 |
| GEL | 12 V | 50 % | 800 |
| Flooded lead-acid | 12 V | 50 % | 400 |
Why a lower sticker price can cost more
Two batteries with the same Ah can store very different amounts of energy over their life. A lead battery of 100 Ah holds 1.2 kWh, but with 50 % usable depth of discharge only 0.6 kWh of it is usable per cycle, and it reaches fewer cycles. A LiFePO4 battery of 100 Ah holds 1.28 kWh, of which 80 % is usable, and lasts several times as many cycles.
With the planning defaults, a LiFePO4 battery at 2.5 times the price of an AGM battery costs about 46 % more per usable kWh up front, but stores about 10 times as much energy over its rated life. Each stored kWh then costs about 75 % less. Whether that pays off depends on how often you cycle the battery: for a weekend camper that rarely drains it, the price per usable kWh matters more than the lifetime figure.
A good offer is one where you checked the price at more than one shop and the data sheet values hold up. For sizing the battery itself, use the battery bank sizer.
Frequently Asked Questions
How do I compare two battery offers fairly?
Compare the cost per stored kWh, not the sticker price or the Ah. Divide the price by the usable energy (Wh × usable depth of discharge) to get the price per usable kWh, then divide that by the rated cycles and the average remaining capacity to get what each kWh you store and use over the battery life costs. The offer with the lower cost per stored kWh is the better deal for a battery you cycle regularly.
What is the difference between Ah and Wh?
Ah is charge, Wh is energy. Wh = Ah × nominal voltage, so a 100 Ah LiFePO4 battery at 12.8 V holds 1,280 Wh and a 100 Ah lead battery at 12 V holds 1,200 Wh. Power stations are usually rated in Wh directly. Compare in Wh or kWh so different voltages do not distort the comparison.
What does usable capacity mean?
Usable capacity is the part of the nameplate energy you can draw regularly without shortening the battery life. As planning assumptions VoltPlan uses 80 % for LiFePO4 and 50 % for AGM, GEL and flooded lead-acid batteries. Replace them with the values from your data sheet if you have them.
Where do I find the cycle count?
In the data sheet of the battery or power station, usually as cycles at a given depth of discharge until a given remaining capacity, for example cycles at 80 % depth of discharge until 80 % capacity remain. Enter that depth of discharge and that end-of-life capacity together with the cycle count. The defaults in the calculator are rough planning assumptions, not manufacturer figures.
Why can a cheaper battery cost more per kWh?
Because a lower price often buys less usable energy and fewer cycles. With the planning defaults, a 100 Ah LiFePO4 battery at 2.5 times the price of a 100 Ah AGM battery costs about 46 % more per usable kWh, but stores about 10 times as much energy over its rated life, so each stored kWh costs about 75 % less.
Does the calculator work for power stations?
Yes. Enter the capacity in Wh from the data sheet and the rated cycles. Most power stations use LiFePO4 cells. If you run mostly AC appliances through the built-in inverter, part of the energy is lost as heat, so set the usable share a little lower.
What does the result leave out?
Charging losses, ageing over time on the shelf, temperature, warranty terms, and the cost of chargers or cables. A battery that sits unused for years ages without reaching its rated cycles, so the cost per stored kWh only applies if you actually cycle it.
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