Battery Capacity Claims in Automatic Watering Kits: How Buyers Should Verify Wh and Runtime

A solar irrigation kit is advertised with a “2200 mAh battery.” The buyer assumes this means the system will run for a certain number of watering cycles on a full charge. But what does 2200 mAh actually tell you? It tells you the battery’s charge capacity at a specific voltage — and if you do not know the voltage, the mAh number is incomplete. Worse, if the battery label says 2200 mAh but the actual cell inside is 1800 mAh, the number is not just incomplete — it is wrong.

Battery capacity misrepresentation is a known issue in small consumer electronics — where a label may state a higher mAh than the actual cell inside delivers. Solar irrigation kits are not exempt from this risk. For buyers, verifying the real battery capacity and translating it into actual runtime is a critical step in sample evaluation.

mAh, Voltage and Wh: What Each Number Means

Three numbers describe a battery:

• mAh (milliamp-hour) — The charge capacity. How many milliamps the battery can deliver for one hour before depletion.
• Voltage (V) — The electrical pressure. A single lithium-ion cell is nominally 3.7V. Three cells in series produce 11.1V.
• Wh (watt-hour) — The total energy. Wh = mAh/1000 × V. This is the number that tells you how much work the battery can do.

The same mAh label means different amounts of total energy at different voltages:

• 3.7V 2200 mAh = 8.14 Wh
• 11.1V 2200 mAh = 24.42 Wh

A buyer comparing two kits, both labeled “2200 mAh,” might assume they have the same battery capacity. If one is 3.7V and the other is 11.1V, the second kit has three times more total energy. The mAh number alone is not a valid comparison unless the voltage is the same.

Why Battery Label Capacity Is Not the Same as System Runtime

Even when the mAh and voltage are accurate, the label capacity does not directly translate to watering cycles. Between the battery and the pump, several things reduce the usable energy:

• Discharge cutoff — Lithium-ion batteries should not be fully discharged. The battery protection circuit (BMS) cuts off discharge at a certain voltage. The exact cutoff depends on the BMS design and cell chemistry — verify with the supplier or by measuring the cutoff voltage during testing.
• Controller overhead — The timer circuit, display (if any), and charge controller all draw current even when the pump is off. This standby consumption reduces the energy available for pumping.
• Pump efficiency — The pump converts electrical energy into water flow and pressure, but not at 100% efficiency. Some energy is lost as heat and mechanical friction.
• Voltage conversion losses — If the pump operates at a different voltage than the battery, the conversion circuit introduces additional losses.

The result: a battery labeled 2200 mAh at 3.7V (8.14 Wh) will deliver less usable energy to the pump than the label suggests. How much less depends on the specific components — measure it rather than estimate.

How to Measure Real Runtime

Do not attempt to reverse-calculate battery capacity from USB charging input — this measures the system’s charging input, not the cell’s usable capacity. Instead, measure the system’s actual runtime under controlled conditions:

Test 1: Continuous pump runtime

1. Start with a fully charged battery.
2. Set the timer to run the pump continuously (or manually activate the pump).
3. Run the pump with the full kit connected (tubing, drippers, water reservoir) and time how long the pump runs before the low-battery cutoff stops it.
4. Record the runtime in minutes. This is the continuous pump runtime on a full charge.
5. Divide by the timer’s watering duration to estimate how many cycles the battery can support.

Test 2: Intermittent pump runtime

1. Start with a fully charged battery.
2. Simulate typical use — spray for 10–15 seconds, release for 5–10 seconds, repeat.
3. Record the total runtime until the battery is depleted.
4. This more closely represents how a home gardener actually uses the system.

Test 3: Standby drain

1. Fully charge the battery.
2. Leave the system with the pump off (timer in standby mode) for 24 hours.
3. Measure the remaining battery voltage or capacity.
4. Calculate the standby drain. This tells you how much energy the controller consumes per day when the pump is not running.

Both continuous and intermittent tests must record the pump model, nozzle, liquid (water), ambient temperature, and the test method used. Without these conditions documented, the runtime numbers cannot be compared across samples or repeat orders.

Battery Indicator Accuracy

(Note: Content on battery indicator accuracy has been merged into this article from a previously separate article.)

A 3-bar or 4-bar battery indicator on a solar irrigation kit typically works by measuring the battery voltage and mapping it to display segments. The problem is that a Li-ion battery’s voltage does not drop linearly during discharge — the voltage stays relatively flat for most of the discharge cycle, then drops steeply near the end.

This means a 3-bar indicator may show “full” for a large portion of the battery’s discharge, then drop suddenly near the end. A segmented battery indicator may remain on “full” for a substantial part of the discharge curve and then drop quickly near the end. The exact display-to-state-of-charge relationship depends on the specific controller and battery system and should be measured on the sample.

To evaluate whether the indicator is useful:

1. Run the system through a full discharge cycle, recording the indicator display and the battery voltage at regular intervals.
2. Note whether the indicator provides meaningful information throughout the discharge, or only at the beginning and end.
3. Check whether the indicator flickers under pump load (voltage sag when the pump runs can cause the indicator to drop a bar, then recover when the pump stops).

The instruction manual should manage customer expectations: “The battery indicator shows approximate charge level. The indicator may show full for an extended period and then drop quickly near the end of the charge. This is normal for lithium-ion batteries.”

How to Document a Claim That Can Survive Repeat Orders

To ensure that the battery capacity claim is consistent across orders:

1. Record the measured runtime from the reference sample — both continuous and intermittent. This is the performance the customer will experience.
2. Record the standby drain from the same reference sample.
3. On repeat orders, re-run the runtime tests. Compare the measured values to the baseline. If the runtime drops significantly, the battery cell may have changed — possibly to a lower-capacity cell from a different supplier. Define your own acceptance threshold based on your product requirements and the baseline data.
4. Retain a reference battery from the approved batch. On repeat orders, compare the new battery’s weight, dimensions, and measured runtime against the reference. A cell that is lighter or smaller may have lower capacity.

A battery label is a claim. The measured runtime is the reality. The buyer’s job is to verify the claim against the reality and document the baseline for future comparison.