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.

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  • Spunjji - Wednesday, November 27, 2013 - link

    Word. This read as an apology to people who already agree with them for how daft the rest of us who disagree are.
  • sevenmack - Wednesday, November 27, 2013 - link

    Now Fearsome, the piece isn't "horribly written" on any objective basis. The issue you and other power users who demand expandable storage have with the piece is that Anand and Brian disagree with your perspective from a technical perspective.

    From where you sit and other power users sit, expandable storage and removable batteries are something you demand because it suits your desire to control your respective user experiences. You are entitled to want greater control over your experiences with your phones, including being able to root your phones, flash new ROMs, or even be able to carry five batteries around with you at all times. You are also entitled to carry a 64-gig MicroSD card if you want. There are phones out there that provide that kind of experience. But most casual smartphone buyers -- who make up most of the market -- don't care one way or another about any kind of customization or about removable batteries or about expandable versus internal storage. They want a reliable phone that looks good (or good enough) and serves their needs for two years. So the expandable-versus-internal storage debate among power users is a nonfactor to them. If Samsung offered a phone without expandable storage or removable batteries, they would just as quickly by that as one with all of those features because they know the Samsung brand name (from all the other consumer products the company makes) and because the company makes reliable phones. [This fact, by the way, is why arguing that Samsung is dominant because it provides phones with expandable meory and removable batteries doesn't wash. It doesn't factor in Samsung's natural market strength as one of the biggest players in consumer electronics, or consider that the competition, including LG and HTC, either are considered second-tier consumer electronics firms or are solely phone makers, the latter being an increasingly endangered corporate species in the smartphone market of today.]

    Even some of us who are power users, including myself, have other considerations in mind; I, for one, want a high-quality phone that is well-designed, that has a mostly-metal body (because I like the feel of aluminum and steel). I have my own cloud server and can upload just about everywhere in the world where I go, and have an array of battery packs that I can use if needed. So the HTC One was the best choice for my wants. And I know other power users (including several in my own family, all who are in the tech field) who have made similar choices; my mother, who has been in tech since the days of the first IBM PC, is an Apple fan, and my sister-in-law, who runs IT services for one firm, is also an HTC One user.

    Ultimately, all of us have a choice regardless of the objective facts. You can choose phones with expandable memory and removable batteries, or choose something different. Anandtech isn't saying that you shouldn't have choice. It is laying out the technical facts that you may choose to ignore or consider. And if you really don't like what Anand and Brian have said, you can also just stop reading Anandtech and read some other site.
  • ATC9001 - Thursday, November 28, 2013 - link

    I understand all the complaints from many of the power users (a site which Anand caters to!), but lets face it, money talks!

    We all want a device tailored to our needs, but we need to understand all the driving forces, and this article addresses the major forces.

    I agree I'd prefer a replaceable battery and upgradable storage over a sealed brick, but in the end I'd prefer an affordable device which doesn't require both! As power users, we're the last to get our cake and eat it too, else we pay for our cake!
  • handynick - Friday, December 13, 2013 - link

    Having a cloud server is useles unless you have a very expensive data plan.
    Many people like premium design, including myself. I could be called a samsung hater for that matter. But HTC One is the best example for not taking advntage from better internal design and structure due to the lack of micro sd slot and removable batery. It.s just a huge premium brick with small screen and small baterry when you consider external dimensions.
  • aknotts - Thursday, March 27, 2014 - link

    The galaxy line has outsold the htcs by a considerable margin. If u think removable battery and expandable storage played no role in this massive upset think again. The consumer has spoken loud and clear htc is just to stupid to hear it.
  • Steven JW FCK - Monday, December 2, 2013 - link

    I 100% agree with you, fearsome

    If you are going to write an article about such a massive issue that has been drawn to your attention by your readers, at least address the down sides of non removable batteries and memory. I mean for instance, 1 water droplet can render you £400 HTC One worthless to you, and you don't mind that? Hmm... Do you consider all Anandtech readers as fortunately wealthy as you?

    And yeah, how on earth did Samsung rise as the largest smart phone manufacturer, when all of it's flagship devices be it budget phone, smart phone, or phablet, have ALL had micro SD cards, and removable storage?
  • sevenmack - Tuesday, December 3, 2013 - link

    Again, Steven, as I mentioned, Samsung is also one of the world's largest consumer electronics firms. Plenty of people have a Samsung television or other device in their homes, and the devices largely work. So when someone walks into a Sprint store or Best Buy, they already have a familiar relationship with Samsung, and chances are, have also bought at least one of its phones already. When you are already dominant in the rest of the consumer electronics market, playing a dominant role in the cellphone arena -- which increasingly is part of the consumer electronics landscape -- becomes relatively easy to do. Samsung could offer a phone without removable batteries or expandable storage and still dominate because of its already-massive reach.

    On the other hand, firms solely focused on telephony have been taking beatings, largely because their focus on one market, along with mindsets that didn't embrace smartphones as consumer electronics, doomed them. This was seen with Ericsson a few years ago and Nokia as well. HTC is now paying the price for its failures a few years ago to expand into consumer electronic; the flop that was the HTC Flyer is one example, while the failure to buy a firm like Vizio is another. HTC could offer a phone with removable batteries and expandable storage (and through both the Desire line and the One Max, already does) and it would still be struggling against Samsung because the HTC name isn't as well known to the average consumer as its bigger rival.

    I know some folks like to use didactic logic in justifying their positions. But in the context of the conversation about the pros and cons of cellphone makers not offering removable batteries or expandable storage, simply offering up a market share example to prove one's point when there are other factors at play just makes you look a tad illogical.
  • aknotts - Thursday, March 27, 2014 - link

    The rise of samsung exactly coincided with other manufacturers decision to drop removable batteries and sd card support. Many people who went samsu g were firmly in the htc camp before htc screwed their customers. Htc screwed up big time. Alot of people bought phones based on recommendations from tech people. No tech person would recommend a phone without a removable battery and no sd card support. The resale value of ur two year old phone with a dieing battery and woefully inadequate storage is significantly reduced.
  • ddriver - Tuesday, November 26, 2013 - link

    Slower? I got a 64gb samsung class 10 micro sd that does ~70 mb/s read and ~22 mb/s write, which is faster than the internal storage of most phones on the market today.
  • SoC-IT2ME - Tuesday, November 26, 2013 - link

    I have that card in my Note 3. It sure doesn't write at 22 MB/s but its fast enough for me needs.

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