Built-In Batteries: a Daft Idea With an Uncertain FutureHaving a gadget’s battery nestled snugly within the bowels of a device has certain advantages. It finally solves the ‘no batteries included’ problem, and there is no more juggling of AA or AAA cells, nor their respective chargers. Instead each device is paired to that one battery that is happily charged using a standardized USB connector, and suddenly everything is well in the world.Everything, except for the devices that cannot be used while charging, wireless devices that are suddenly dragging along a wire while charging and which may have charging ports in irrational locations, as well as devices that would work quite well if it wasn’t for that snugly embedded battery that’s now dead, dying, or on fire.Marrying devices with batteries in this manner effectively means tallying up all the disadvantages of the battery chemistries and their chargers, adding them to the device’s feature list, and limiting their effective lifespan in the process. It also prevents the rapid swapping with fresh batteries, which is why everyone is now lugging chunky powerbanks around instead of spare batteries, and hogging outlets with USB chargers. And the task of finding a replacement for non-standardized pouch cell batteries can prove to be hard or impossible.Looking at the ‘convenience’ argument from this way makes one wonder whether it is all just marketing that we’re being sold. Especially in light of the looming 2027 EU regulation on internal batteries that is likely to wipe out the existence of built-in batteries with an orbital legal strike. Are we about to say ‘good riddance’ to a terrible idea?Not Very ProThe Nikon EL-EN15 battery.To further rub in how much of a terrible idea built-in batteries are, one only has to look at professional equipment, particularly in the audiovisual world. Whether we are talking about DSLRs, mirror-less cameras, or professional video cameras, they all have as standard feature the ability to quickly swap batteries. Nikon and Canon cameras use a range of proprietary-but-standard Li-ion batteries, with Sony’s video camera batteries also used on portable studio lighting. For the super-expensive Red video cameras you can use either the massive Redvolt batteries that dangle off the side or a power adapter.The reasoning here is simple: when you are doing a photo or film shoot you do not have time for charging, so you load up with a stash of charged batteries beforehand. As the current battery becomes drained, you pop open the battery hatch or detach the current pack and slam in a fresh battery before resuming. During moments of downtime you can put the drained batteries on the charger that you have squirreled away somewhere. This way you stay wireless and charged with zero fuss, and if you have enough batteries, zero downtime.Even within the era of budget photo and video cameras you’d be able to do this. When it comes to my own JVC camcorder and Canon IXUS 100 IS point-and-shoot camera, both offer this feature, even if the battery swapping experience doesn’t feel as premium as with the Nikon D7200 DSLR and its EN-EL15 batteries that is used for more serious occasions. Swapping batteries with the DSLR in particular is as easy as swapping SD cards, which is to say a matter of seconds.One might get the idea here that the main reason to stuff a pouch cell somewhere inside the device is mostly a cost-saving measure, as it omits the battery terminals and ejection mechanism for the pack.Battery DecayAnother reason why having a built-in battery with a multi-thousand-Euro DSLR would be a terrible idea beyond the insanity of having to ‘charge the DSLR’, is that the battery will be dead long before even the warranty on the DSLR has expired, especially if you are an avoid shooter. Even if you do not use a device that much, the fact of the matter is that lithium-ion cells begin to degrade as soon as they have been manufactured. This may be acceptable in a €1,000+ smartphone when people buy a new one every other year anyway, but becomes a problem when you’d like to use a device for much longer.A good summary of the how and why of lithium-ion batteries (LIB) can be found in this IEEE review article by Wiljan Vermeer et al. from 2021. The three main aging mechanisms are:Loss of Lithium Inventory (LLI).Loss of Active Material (LAM).Conductivity Loss (CL).There are multiple ways in which each type of aging can occur, with most requiring the cell to be charged and discharged, as this inflicts mechanical and other types of stress. When it comes to storing LIBs, we enter the territory of calendar aging. This has an irreversible and reversible component, the former being impacted by three components: the state of charge (SoC), temperature, and time.Calendar aging of NMC Li-ion cells at 50 ℃ and at various SoCs. (Credit: Wiljan Vermeer, IEEE, 2021)What this tells us is that although you can affect LIB calendar aging, it’s a pretty inevitable aspect of their chemistry. This is true even in the case of the lithium-polymer (LiPo) LIB type batteries with its polymer electrolyte. This effectively means that charging the battery in a device to 80% instead of 100% will give it some more life, but you’d have to drop down to 50% or less to see the big gains. It’s also highly advisable to keep the battery relatively cool, which is where fast-charging is a terrible idea, especially as the resistance of the battery goes up due to aging.While the exact mechanisms behind calendar aging are still being investigated, it’s likely that the layer that forms at the electrochemically unstable electrolyte-electrode interface (SEI) restructures to prevent the transfer of lithium ions, effectively increasing the measured resistance via the CL aging path.In addition to calendar aging you have the charge-discharge cycle-based aging mechanisms, which not only affects the SEI, but also causes mechanical expansion of the graphite anode material, which leads to both the LLI and LAM aging paths. When you then add in the typical charging method for gadgets like smartphones using a LIB-based powerbank, you end up with double the charge-discharge cycles over simply slotting in a fresh battery.End Of The RoadReplacing the battery in the Samsung Galaxy Nexus. (Credit: Maya Posch)Beyond larger electronic devices, pouch cell LIBs are now integrated in countless more gadgets, from lamps to Bluetooth speakers. To address the sheer volume of these built-in LIBs, the EU’s Battery Regulation will begin to enforce its removability and replaceability requirements starting on 18 February of 2027.The batteries which we discussed in this article fall under so-called ‘portable batteries’, meaning that it weighs less than 5 kg and is not used for an electric vehicle. These are required to make it possible for the end user to replace and remove, all without damaging or destroying the battery or the device, and without requiring any special tools. There are some partial safety-related exceptions where a professional can do said replacement, while a full exception is limited to a number of very specific device categories.What exactly the fallout of this change will be remains to be seen, with manufacturers likely starting to adapt their products throughout 2026. Devices like smartphones, game controllers, but also Bluetooth speakers, wireless mice and portable game consoles will all be affected, so it’ll be interesting to see what approach we will see here.Perhaps most of all what it might mean for standardization of cells and batteries, as every device that’s put on the market in the EU must have spare batteries available for reasonable cost for five years after it stops being sold. Clearly this would be cheaper if the same battery just got used for decades, somewhat like the veritable AA cell and today’s 18650 and similar formats.So Many StandardsThe process of standardization is a rough one, with sometimes the legislature leaning into the issue after consultation with a requirement, as with USB-based chargers. Other times the market simply picks something that’s readily available and does the job. One example of this is the Nokia BL-5C battery and its variations, which was quite prevalent due to Nokia using it for its phones and other platforms like the N-Gage. Consequently third-party manufacturers made their own compatible versions for use in a wide range of devices.The Nokia BL-5C Lithium-Ion battery, this one from a Nokia N-Gage. (Credit: Evan-Amos)While the BL-5C is still fairly large, at 53 mm x 34 mm and a thickness of 6 mm, point and shoot cameras as well as action cameras feature a range of smaller batteries, with the Canon NB-4L as used in the IXUS point and shoot cameras providing more than 750 mAh in a 35 mm x 40 mm package and a similar 5.9 mm thickness. The third-party replacements that I got of the NB-4L claim to provide 1,200 mAh, as modern LIBs tend to have more capacity within the same form factor due to more refined manufacturing.Interestingly, even rechargeable AA-sized cells aren’t limited to NiMH chemistry any more, with Li-ion options now available yet still providing the 1.5 V one would expect. This does require a bit of electronics in the cell, and results in them having a capacity that’s similar to that of NiMH AA cells, while suffering all the aging issues of any other LIB in addition to the limited number of charge cycles. Assuming that the 1.2 V of NiMH cells is acceptable, then devices could accept AA or AAA NiMH cells.Of note here is that none of this means that having a power input port for charging the battery or cell inside the device itself is no longer possible or allowed. Depending on the device manufacturer, the new EU regulations should mean little difference for the end user, other than having the option to pop open each device to extract and replace the battery. This could mean that wireless mice and Bluetooth headsets will soon feature an alternative to sticking in that charge cable and have the device be mostly useless until its built-in battery has soaked up sufficient juice.Although this is an EU-only thing, it’s likely to come to every other part of the globe as well.hackaday.com/2025/10/23/built-…
