What does your energy really cost?

Two stations at the same price can cost anywhere from one to three times as much in use. What matters is not the purchase price but the cost of every kWh the battery will deliver before it ages. This tool works out that real cost and ranks the catalogue accordingly, to reveal true value for money.

The formula

Cost per kWh = price ÷ (number of cycles × capacity in kWh). One cycle is a full charge and discharge; manufacturers rate the number of cycles until about 80 % of the original capacity remains. We also derive the cost of a full charge and the total energy delivered over the lifespan.

What it reveals

• An LFP (LiFePO4) battery costs more upfront but lasts 3 to 6 times more cycles than a classic Li-ion (NMC). Over the lifespan, its energy is often far cheaper.
• A cheap model with few cycles can turn out to be the most expensive per kWh, once worn out and replaced.
• You can enter your own values (price, capacity, cycles) to compare a model that is not in the catalogue.

Who it is for

This tool is for people who keep their gear for several years and want to invest wisely: regular campers, remote workers, households equipping against outages. The figures are estimates (real lifespan depends on temperature, depth of discharge and care), but they move the decision from the sticker price to the real cost, where the true bargains hide. Amazon stations, whose price we do not display, are excluded from the ranking.

What cost per kWh does not tell

Cost per kWh is the best single indicator, but a few factors refine the decision further. The warranty (often 3 to 5 years, sometimes expressed in cycles) protects your investment and says a lot about the maker’s confidence. Depth of discharge matters too: never running down to zero, avoiding heat and prolonged full charges slows ageing well beyond the theoretical figures.

Finally, think about real use. A battery used every day quickly pays off its LFP premium; a backup battery used three times a year will never reach the end of its cycles, and the priority criterion then becomes low self-discharge and calendar longevity. The tool gives you the hard baseline; add your own usage frequency to make the call.

We have seen hundreds of batteries over ten years, and the same lesson keeps returning: the purchase price misleads, the cost per kWh reveals. Use this ranking to spot the real bargains, then check the chemistry (LFP preferably) and the warranty on the page of the model you are eyeing before you decide.