If you are new to Li-ion batteries and standards compliance in the context of IEC 60601-1, the area can be confusing - largely because there is some messy history. Normally with a high risk part such as this you can buy it off the shelf, all nicely certified, well specified, just plug and play.
To a large extent battery manufacturers have done their job well, especially if you are dealing a reasonably well known, quality battery maker. The weak point is mostly on the standards and third party testing. It is improving, and perhaps in a few years an article like this will no longer be needed.
OK, before we start some basic terms.
Standards refer to “primary” and “secondary” cells or batteries - translated this means “non-rechargeable” and “re-chargeable” respectively.
Standards also refer to “cell” and “battery”. Normally lay people mix up battery and cells, while us experts know that “battery” means two or more cells. Well, forget that. For IEC standards, a “battery” means one or more cells together with any necessary protective features. Any sizable cell will normally have a PCM or Protection Circuit Module, so even a single cell with a PCM is referred to as a “battery”.
This article is intended for a re-chargeable cells with a size large enough to need a PCM, i.e. secondary batteries. Anecdotally, the threshold for this seems to be around 50mAh, although no literature has been found to support this. This article, by the way, is all anecdotal - please use it to power your own research, but not as a resource itself.
Now for some basics on Li-ion safety.
Li-ion is generally safe compared to the original lithium metal batteries. However, under overload, short, overcharging and age, the Li-ion can convert to metal and become highly flammable. In order to protect against this, most cells will have three protection features inside the cell, including a PTC for overcurrent, a pressure switch for overcharging (triggered by gas production), and finally a vent (weak point) to release pressure in case the other two fail.
But … these protection features are not what we would call super reliable. They might work, say, 19 out of 20 times. I have no idea of the actual value, only that it’s nowhere near the normal reliability we would expect for a safety feature associated with fire.
Thus, once the cell gets to a certain size, say >50mAh, most manufacturers will fit a PCM. This is a small electronic circuit that watches the cell voltage, charge and discharge currents and disconnects the battery if anything exceeds the limits. It’s usually built into the pack, a small PCB at the top which can sometimes be seen if the final wrap is clear. There are many dedicated ICs that can perform this function with just a few external components, and there are ICs for multi-cell packs that can watch each cell individually. The PCB also often contains a 10k NTC thermistor - more on that later.
This “battery”, which contains cell(s) with protective features (PTC , PS, PV) plus the PCM is what you will typically find on the market today. As long as the end product manufacturer makes sure the charging circuit fits within the normal condition limits as specified by the battery manufacturer (currents, voltages, profiles, temps) then the overall system is safe in normal and single fault condition. Plug and play.
So far so good. But in the modern world, for high risk things like preventing fire it is not enough to trust a spec sheet: it has to be verified in design and production, with regulatory records. To avoid that every end user has to audit the battery manufacturer, we normally rely on third party certification.
This is where things fall off the rails.
Third parties are generally good at all the cell side of things - cells normally have a bunch of stress tests thrown at them to show they are unlikely to explode or catch on fire. However, for larger cells the charging voltage is normally limited during testing to the values specified by the manufacturer, for example 4.35V for a typical 3.7V cell.
Why?
My guess - historically, UL were the market leader, UL1642 certified cells were (are?) the defacto standard. Knowing that larger cells can occasionally explode if overcharged, their approach was to test to the limits specified by the manufacturer (e.g. 4.35V) and then “list” the cells using these limits, requiring that the end user would ensure these limits are not exceeded in normal and single fault condition.
End product manufacturers however, not being aware of the dangers, often missed the “single fault condition” part and designed chargers around normal condition only, typically 4.25V. In fact, the only way to cover the single fault condition successfully is to have a fully independent circuit between the charger and the battery, something that is not intuitive for an end product designer. Moreover, in the case of a series of cells (e.g. 7.2V, 14.8V packs) it is not possible to monitor the individual cell voltage external to the pack, so UL’s approach was actually an impossible to meet.
Battery manufacturers knew this, and started fitting PCMs to packs to handle the single fault condition. It’s perhaps a rare case where manufacturers got ahead of the agencies, which in turn clearly indicates that Li-ion is definitely dangerous stuff. If it was all just theoretical, there is no way the PCMs would be fitted unless pushed by the agencies.
It’s also possible that agencies knew about the importance of PCMs but were reluctant to accept electronic based protection: historically “protection” is in the form of fuses, circuit breakers, optocouplers, insulation, earthing, where the protection itself can be tested for various aspects reliability. Electronic circuits don’t lend themselves to this kind of verification. In the real world though, the PCM is a very simple circuit and modern electronics is generally reliable - like 10-9 events per year kind of realm - in practice a PCM is far more reliable than a fuse or circuit breaker.
That of course is history, and standards and third parties are catching up. The latest standard IEC 62133-2:2017, which is dedicated for re-chargeable Li-ion cells and batteries, does allow for testing that includes the PCM.
However this standard was only released in 2017, so much of the documentation on Li-ion batteries may pre-date this. The older standard IEC 62133 does not reliably test the PCM, nor does UL1642 or UL2054 listings.
Confusingly, IEC 62133-2 can be used for both cells and batteries. If the report is just for the cells it won’t cover the PCM and various other tests. By using the same standard number for cells and batteries means that users need to look into the report to figure out what is going on. I guess that in the future we may see a new standard covering a “battery pack”, to mean an object that has all the protective features built in, that the end user can really just plug and play.
A side issue is that battery packs are often custom designed, and there are a wide range of sizes and shapes available, some are fairly specialized and low volume. Forcing manufacturers into third party certified pack route may not be feasible. Thus a real long term solution may also see a consolidation and standardization of the available pack size, ratings, and physical shape, which itself may not be a bad thing.
OK, with all that in mind, how to deal with Li-ion batteries and IEC 60601-1?
For secondary batteries, IEC 60601-1/A1:2012 Clause 15.4.3.4 refers to an compliance with IEC 62133. Since this is undated, technically the latest edition should be used, which is IEC 62133-2:2017. It’s also important to note that the standard refers to “secondary batteries” not “secondary cells”, which in turn means that the PCM, if required for safety, must be included in the testing.
Note that if you are reading the earlier version of IEC 60601-1:2005, it has an incorrect reference to IEC 60086-4 which is only for primary or non-rechargeable batteries. This was corrected in A1:2012.
When you ask battery manufacturers for evidence of compliance they may provide a few different things:
Some may provide reports for the old IEC 62133:2012. This standard may be OK for the cell, but it may not cover the PCM.
Some manufacturers may point to UL1642 listing. This is an older standard, and not IEC aligned, but is reasonably seen as equivalent to IEC 62133. However, it again it is just for the cell and does not cover the PCM.
If you are lucky, the manufacturer might provide a report for IEC 62133-2:2017 which is the the newer version and covers the PCM. However, you need to check the report (not just for example, the CB certificate) to make sure it is for the battery pack and not just the cells. Also reports (and CB Certificates), only cover the samples tested, and don’t cover regular production. Legally, you need to be covered for design and production. As such, even if you have a report, it’s recommended to ask for a declaration of conformity, since a properly prepared declaration covers both design and regular production. Make sure the declaration refers to IEC 62133-2:2017 (dated), and make sure it covers the pack with the PCM, not just the cells.
If you are really lucky you might get:
UL listing to UL62133-2:2020. This UL standard is fully harmonized with IEC 62133-2:2017 and covers the PCM, and if the part is UL listed this means it includes a factory inspection (i.e. production is covered)
any other private certification marks such as TUV SUD, TUV Rh, VDE etc, which has the latest standard (IEC 62133-2:2017) and includes factory inspection.
These last two are truly plug and play. However, it is expect these will take a while to get popular.
In the mean time, what to do if really like the pack but the evidence is weak and may not cover the PCM?
The first point is to check if a PCM is fitted. This is usually indicated in the specification sheet.
Next, there are a few options, which could be taken in combination:
Trust the manufacturer: if it is a well known brand this might be enough for some users
Ask the manufacturer for a declaration of conformity to IEC 62133-2:2017 covering the battery pack with the PCM installed (as above)
Periodically inspect and test packs for implementation and correct operation of the PCM. Note this needs to be done in a safe way considering the risks of exploding batteries.
If there is no PCM or the implementation cannot be confirmed, it’s also possible to fit your own PCM external to the pack, provided that it is single cell only.
If the cell is small enough that a PCM is not required, note that this still needs evidence. The cell certification should be compatible with the voltage/current available in fault condition from the end product. For example, if the charging IC is run off a 5V/500mA USB supply, then if the charging IC fails, these would be the most expected in fault condition. If you have say UL1642 cells certified to 5V/1A, then that might be enough.
Apart from above, from experience end product manufacturers sometimes mess up the charging characteristics. Most charging ICs are flexible and there are several parameters which can be set by external components. It’s always worth having an independent engineer double check the calculations. Wireless chargers have extra complexity and worth to double check the charging parameters and profile is as expected.
In 2007 the Japanese organisation JEITA issued a guideline on temperature limitations for Li-ion charging. Many chargers now work with these limits, using an NTC that is situated close to or inside the pack. It is recommended to use this feature if possible to maintain battery life and for additional safety (less chance of the other protective features being activated). Many packs have a third lead with a 10k NTC fitted for this purpose.
These last two points are technically covered by IEC 60601-1 Clause 4.8, which requires that components are used within specification. However, not all test agencies will check the detail, so it’s worth double checking internally with an independent engineer.
In addition to IEC 60601-1, most people would have heard of UN 38.3 which covers shipping. I’m not an expert on this, but I assume a declaration might be needed before agencies like DHL, FedEx, UPS etc will accept batteries for shipping.
There is also an EU battery directive. Again it is not an area of expertise but from memory there is a requirement to provide a practical method for removing the batteries for disposal. In other words, simply saying “dispose of according to national regulations” in the IFU may not be enough.
A final reminder! All information here is provided to help designers get started, but should not be used as a formal reference. Always check the source regulations, standard etc for the final decision, and if necessary engage qualified experts.