There's been a lot of talk lately about our position on removable storage and removable batteries in smartphones. Most of the discussion has centered around what we've said in podcasts or alluded to in reviews, so we figured it's a good time to have the complete discussion in one central location.

Let's get through the basics first:

All else being equal, removable storage and user replaceable batteries aren't inherently bad things. In fact, they can offer major benefits to end users. 

The key phrase however is "all else being equal". This is where the tradeoff comes in. On the battery front, the tradeoff is very similar to what we saw happen in notebooks. The move away from removable batteries allows for better use of internal volume, which in turn increases the size of battery you can include at the same device size. There are potential build quality benefits here as well since the manufacturer doesn't need to deal with building a solid feeling removable door/back of some sort. That's not to say that unibody designs inherently feel better, it's just that they can be. The tradeoff for removable vs. integrated battery is one of battery capacity/battery life on a single charge. Would you rather have a longer lasting battery or a shorter one with the ability the swap out batteries? The bulk of the market seems to prefer the former, which is what we saw in notebooks as well (hence the transition away from removable batteries in notebooks). This isn't to say that some users don't prefer having a removable battery and are fine carrying multiple batteries, it's just that the trend has been away from that and a big part of the trend is set based on usage models observed by the manufacturers. Note that we also don't penalize manufacturers for choosing one way or another in our reviews.

The tradeoffs are simple with an internal battery, the OEM doesn't need to include a rigid support structure on the battery to prevent bending, and doesn't need to replicate complicated battery protection circuitry, and can play with alternative 3D structures (so called stacked batteries) for the battery and mainboard as well. Personally, I'd rather have something that lasts longer on a single charge and makes better use of internal volume as that offers the best form factor/battery life tradeoff (not to mention that I'm unlikely to carry a stack of charged batteries with me). It took a while for this to sink in, but Brian's recommendation to charge opportunistically finally clicked with me. I used to delay charging my smartphone battery until it dropped below a certain level and I absolutely needed to, but plugging in opportunistically is a change I've made lately that really makes a lot of sense to me now.

The argument against removable storage is a similar one. There's the question of where to put the microSD card slot, and if you stick it behind a removable door you do run into the same potential tradeoff vs. build quality and usable volume for things like an integrated battery. I suspect this is why it's so common to see microSD card slots used on devices that also have removable batteries - once you make the tradeoff, it makes sense to exploit it as much as possible.

There's more to discuss when it comes to microSD storage however. First there's the OS integration discussion. Google's official stance on this appears to be that multiple storage volumes that are user managed is confusing to the end user. It's important to note that this is an argument targeted at improving mainstream usage. Here Google (like Apple), is trying to avoid the whole C-drive vs. D-drive confusion that exists within the traditional PC market. In fact, if you pay attention, a lot of the decisions driving these new mobile platforms are motivated by a desire to correct "mistakes" or remove painpoints from the traditional PC user experience. There are of course software workarounds to combining multiple types of storage into a single volume, but you only have to look at the issues with SSD caching on the PC to see what doing so across performance boundaries can do to things. Apple and Google have all officially settled on a single storage device exposed as a single pool of storage, so anything above and beyond that requires 3rd party OEM intervention.

The physical impact as well as the lack of sanctioned OS support are what will keep microSD out of a lot of flagship devices. 

In the Android space, OEMs use microSD card slots as a way to differentiate - which is one of the things that makes Android so popular globally, the ability to target across usage models. The NAND inside your smarpthone/tablet and in your microSD card is built similarly, however internal NAND should be higher endurance/more reliable as any unexpected failures here will cause a device RMA, whereas microSD card failure is a much smaller exchange. The key word here is should, as I'm sure there are tradeoffs/cost optimizations made on this front as well. 

The performance discussion also can't be ignored. Remember that a single NAND die isn't particularly fast, it's the parallel access of multiple NAND die that gives us good performance. Here you're just going to be space limited in a microSD card. Internal NAND should also be better optimized for random IO performance (that should word again), although we've definitely seen a broad spectrum of implementation in Android smartphones (thankfully it is getting better). The best SoC vendors will actually integrate proper SSD/NAND controllers into their SoCs, which can provide a huge performance/endurance advantage over any external controller. Remember the early days of SSDs on the PC? The controllers that get stuffed into microSD cards, USB sticks, etc... are going to be even worse. If you're relying on microSD cards for storage, try to keep accesses to large block sequentials. Avoid filling the drive with small files and you should be ok.

I fully accept that large file, slow access storage can work on microSD cards. Things like movies or music that are streamed at a constant, and relatively low datarate are about the only things you'll want to stick on these devices (again presuming you have good backups elsewhere).

I feel like a lot of the demand for microSD support stems from the fact that internal storage capacity was viewed as a way to cost optimize the platform as well as drive margins up on upgrades. Until recently, IO performance measurement wasn't much of a thing in mobile. You'd see complaints about display, but OEMs are always looking for areas to save cost - if users aren't going to complain about the quality/size/speed of internal storage, why not sacrifice a bit there and placate by including a microSD card slot? Unfortunately the problem with that solution is the OEM is off the hook for providing the best internal storage option, and you end up with a device that just has mediocre storage across the board.

What we really need to see here are 32/64/128GB configurations, with a rational increase in price between steps. Remember high-end MLC NAND pricing is down below $0.80/GB, even if you assume a healthy margin for the OEM we're talking about ~$50 per 32GB upgrade for high-speed, high-endurance internal NAND. Sacrifice on margin a bit and the pricing can easily be $25 - $35 per 32GB upgrade.

Ultimately this is where the position comes from. MicroSD cards themselves represent a performance/endurance tradeoff, there is potentially a physical tradeoff (nerfing a unibody design, and once you go down that path you can also lose internal volume for battery use) and without Google's support we'll never see them used in flagship Nexus devices. There's nothing inherently wrong with the use of microSD as an external storage option, but by and large that ship has sailed. Manufacturers tend to make design decisions around what they believe will sell, and for many the requirement for removable storage just isn't high up on the list. Similar to our position on removable batteries, devices aren't penalized in our reviews for having/not-having a removable microSD card slot.

Once you start looking at it through the lens of a manufacturer trying to balance build quality, internal volume optimization and the need for external storage, it becomes a simpler decision to ditch the slot. Particularly on mobile devices where some sort of a cloud connection is implied, leveraging the network for mass storage makes sense. This brings up a separate discussion about mobile network operators and usage based billing, but the solution there is operator revolution.

I'm personally more interested in seeing the price of internal storage decrease, and the performance increase. We stand to gain a lot more from advocating that manufacturers move to higher capacities at lower price points and to start taking random IO performance more seriously.



View All Comments

  • sevenmack - Wednesday, November 27, 2013 - link

    Except that the "quick swap" isn't that quick. And, from my experience, you also have to have a good external charger to make sure that the external batteries, be they OEM or non-OEM, are fully charged. You can end up with a secondary battery that isn't fully charged and will lose that charge quickly after taking a bunch of photos.

    Again, everyone has a choice of phones with removable batteries and phones without them. If you want the former, then buy phones that offer that option and vice versa.
  • vortexmak - Wednesday, December 4, 2013 - link

    A quick swap really is quick. It takes me a minute to power off, replace and power on my phone.

    We have to be vocal, cause the manufacturers think that no one wants phones with removable batteries. Thank God Samsung still knows the market
  • sevenmack - Thursday, January 16, 2014 - link

    Except that it isn't, especially if you are in conditions such as airports or in the middle of remote areas where you can't really just stop, turn off the phone, search for the battery, take the cover off the phone, and then do the swap. To you, that's quick. To me as a power user, and to most mainstream users, that's a lot of time for not much gain.

    In the long run, the best solution is for better battery development, better software development (in order for power to be used more efficiently) and even better decisions by power users when it comes to operating smartphones. The last point is also true for storage. If so many power users weren't engaging in what can be best called digital hording, holding on to every megabyte instead of backing up data properly and deleting that which is no longer useful or necessary, then the storage given (especially when one gets 32 gigs to work with) would be more than enough.
  • zmatt - Wednesday, November 27, 2013 - link

    I'm sorry but this post reeks of arrogance. There are pros and cons to both sides and as the sales figures show people prefer removable batteries and expandable storage to locked down devices. It's no surprise the enthusiasts agree as well. We want more control over our devices. The benefits to removable batteries and sd slot are too obvious to state here but I will say that this, the hard stance that Anandtech and Anand himself has taken on this biased view has hurt my opinion of the site irreparably. It shows a lack of journalistic integrity and whatever the cause, be it personal bias or a thinly veiled anti-Samsung stance it doesn't matter. You have done a massive disservice to the community and have betrayed your user base. Reply
  • spronkey - Thursday, November 28, 2013 - link

    I strongly disagree with almost all points here. Anand might be drinking a bit too much Apple cool-aid these days :/

    1) Removable batteries do not dictate form factor
    2) Protection circuitry is necessary regardless of removable vs not, and battery-level protection circuits are very small in size
    3) Costs for removable batteries are already hugely inflated by manufacturers, and integrated battery replacement costs are even worse. $80 to replace a tiny battery? The batteries cost far less than $10 to produce. Ridiculous.
    4) I'd love to see a standardised small form factor Lithium-based battery. You know, like AA. And usable cross-device. That way, I could take a battery from my camera, stick it in my phone, flashlight etc, all using readily-available chargers. This also encourages competition.

    On MicroSD, again, I disagree that the "better" solution is cheaper inbuilt upgrade prices. The better solution is *both*, and, ideally, upgradable inbuilt storage!

    In a year's time, there's a good chance that 64GB card will cost less than it does now. I've got $200 to spend right now. I'd rather spend it on a phone with fast CPU and good camera, but with small storage, than spend it on a lesser phone with a large NAND. That way, a year down the track I've got a better phone with an extra 64GB of storage (for the obvious stuff - music, video, and photo).

    It's also really damn handy to have a removable card - that way if I want to go and print a photo, for example, I can just pop the card out of my phone, and plug it in to one of those photo print stations. No cables. Or pop it into an SD adaptor and use it with my dSLR or video camera, then pop it back into my phone (or tablet, let's not forget tablets here) and view that content on a larger screen while I'm out and about.

    I think the important thing to remember here is that for 80% of people, high-performance NAND is not something that gives any real benefit - the majority of their storage requirements are serially-accessed media files anyway! Who cares if the bits in my photos can't be randomly accessed super quickly :/
  • spronkey - Thursday, November 28, 2013 - link

    I'd also just like to reiterate that the whole C vs D drive thing is crap. You can get around it very easily by saying that MicroSD cards can be used for media files only. All the media player apps have metadata libraries that simply point to the actual storage location anyway. Reply
  • StrangerGuy - Thursday, November 28, 2013 - link

    You forgot the part how your phone can't play MP3s and load images from your crappy SD card with *only* 10MB/s reads which apparently is too slow for consumers according to AT. Reply
  • Ev1lAsh - Thursday, November 28, 2013 - link

    Love the site and agree with the removable battery argument (even though I've put in a bigger battery for my phone). But saying removable storage is not important because there SHOULD be sufficient space is a fallacy. Its like saying console games should be cheaper so lets continue paying the current price -how are OEMs to know what we what, especially the masses who don't frequent sites like this (and leave comments), or know what is possible with current tech.
    I'm a frequent flyer so I need that extra space, and sadly I'll only get it caked in when (no offence to ye) review sites stop bigging up pixel density and phone dimensions / thinness (improvements in these are academic now anyway) and focus on storage space and battery life.
    And yes ordinary users want these too, I got my Mum a smartphone and she was really pissed her phone didn't last a week on standby like her old phone did. To her the technology wasn't ready if she had to compromise on this; she only wanted a touch screen -apps mean nothing to her.
  • HansCPH - Thursday, November 28, 2013 - link

    In this long comment section, the authors has not seen cause to react or respond, even a little, to protests from users on the acclaimed benefits of:
    1. not making user-replaceable batteries in smartphones
    2. not making SD expandable file storage in smartphones.

    When Brian Klug ventured this road a while back alone, at least he tried responding, -initially !

    The present double-authored fashion statement on the BAT/SD issue, stands as is.

    Anandtech has become the ANA (American Humane Association — the grantor of the familiar “No Animals Were Harmed” trademark accreditation seen at the end of film and TV credits) of tech, and curled up with (some of) the producers.
  • HansCPH - Thursday, November 28, 2013 - link

    ANA should be AHA Reply

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