Unfortunately, changing to a new battery model from a new supplier is not as straightforward as most people think. Careful lithium battery validation is required in order to ensure they don’t lead to many failures.
In many cases, the majority of failures on electronic devices actually come from the battery. A battery that is a poor fit for your device, or with very inconsistent performance, will result in customer dissatisfaction, returns, and brand damage. It may even lead to recalls and perhaps lawsuits and damages in the case of accident and injury.
Validating a new battery for an existing product is, in a way, like validating a new product. In most cases, these steps must not be skipped:
- Confirm the specifications that correspond to the needs of the product
- Ensure the battery fulfils those specifications (through testing)
- Track performance over time (batch check)
Keep reading for an introduction to the kind of battery testing we suggest when sourcing a new lithium-ion battery for your existing product…
Which battery tests to run?
Important question that will impact the testing plan: do your product’s users tend to do mostly partial discharges or full discharges? The way to test the batteries will, ideally, replicate that particular user pattern.
We usually suggest testing for:
- Maximum output current
- Protection of circuit
- Over voltage
- Ageing (sometimes 100% of batteries are charged & discharged continuously for 1 week)
- Battery performance in different temperatures
- Battery self-discharge
And it is also helpful to dismantle a battery to check its components (e.g. size of the wires), and then to confirm none of that changes from one batch to another. Please note, this does not mean opening the battery up to expose its liquid electrolyte, which could lead to injury.
At Sofeast we prepare customized testing plans for our client’s specific needs, and we often test to UN38.3 standard for safe shipping – this standard basically includes the above tests but also tests that replicate the conditions the battery will endure during shipping, such as:
- Altitude (low-pressure conditions)
- Shock impact
- Crush testing
- Drop test
Monitoring battery life after 6-12 months of usage
Electronic products need a battery whose performance is going to satisfy the user for a reasonable time, probably at least the warranty period if not more depending on the cost and perceived value of the product.
If one of the failure modes observed during testing is a quickly dwindling battery lifetime, it is important to test the output impedance, which may be what leads to shorter battery life. (It may not be an issue coming from battery capacity.) Testing the impedance on batteries is a pretty fast job, so testing 100% of the samples is usually not an issue.
To test battery life, there is only one way – test the charge/discharge cycle of the batteries; for example, go through 500 cycles and check if the real capacity is still over 80% of nominal capacity.
Typically, good long-lasting lithium batteries for always-on applications such as in a large iPad type tablet should have at least 850 charge/discharge (C/D) for the same way they tested which is fine. 850 is the typical but high-end batteries can go up to 1000 or more C/D with 60% remaining at the end.
What other factors may be contributing to a short battery lifetime?
- Battery load… in terms of drawing current
- How many apps are running in the background and how much power they are using
- Design and quality of battery components; for example, low-cost alloy components used in the battery that hold less charge than those of a higher quality
- Poor design and construction and manufacturing quality of batteries contribute to a shorter lifetime
- Some battery management ICs that are having issues with memory cache will keep running and draining the battery
Testing battery reliability
In general, for ensuring that the battery used in a design will be reliable you need to take these actions:
- Create a reliability test plan for a battery as a component which includes charge and discharge
- Include battery management circuitry that keeps monitoring the health of the battery continuously and will, for example, automatically shut down the battery if the normal operating conditions have changed. For example over temperature, over voltage, and over current and shorting.
Where to start?
For lithium battery validation as a first step, it’s good if the battery supplier provides you with their test data. The battery specification sheet is a very helpful document to obtain from them and will, hopefully, provide the information you need to assess whether batteries are genuine, good quality, etc.
There is, of course, a risk that some of the data are not truthful. During an audit of the battery factory, it is good to double-check that they really do tests, that the records make sense, etc. For example, are there signs that some batteries went all the way to burning/exploding? (That’s a good sign.)
If batteries are made by, say, Panasonic, you can ask them directly to confirm whether the battery codes you see are genuine, too.