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There are lots of consumer devices that run on rechargeable batteries and have those batteries non-removable without disassembling a device. The most notable example is I guess an iPhone.

Making a battery non-removable has these advantages:

  1. simpler case - no need for the door that would otherwise need to be strong enough to survive careless operations by the user

  2. better case sealing

  3. tighter packing of the battery into the case allows for more space for other components or smaller case

  4. users are forced to use service shops that can generate money for the manufacturer through "authorization" programs

Yet none of these reasons seems to have any electrical design basis.

Are there electrical design reasons for making rechargeable batteries non-removable?

Olin Lathrop
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sharptooth
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    No. There are no good electrical reasons. The main reason is to force users to reply on first party servicing to fix any problems. If they let users change the battery, then they wouldn't have the guaranteed revenue stream in two years when the battery fails. – Rocketmagnet Jul 11 '12 at 12:24
  • @Rocketmagnet: Actually I can't fully agree. Take Nokia - it sells branded batteries at its brand stores and there're third-party replacements available. I'm pretty sure the brand batteries generate good income to Nokia. I could buy a third-party battery, but I'm not that sure it's as reliable and as performant as Nokia branded one (and I know that a Nokia branded battery is reliable and performant since I have once initially in my phone). – sharptooth Jul 11 '12 at 12:38
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    Sure, they make some money from selling batteries, but they could have more if they could also charge people for replacing them. – Rocketmagnet Jul 11 '12 at 12:48
  • I currently have a non-removable coin-cell clock backup battery in a product. At the time, I couldn't FIND a -40 to 85 degC coin cell without solder tabs. I didn't want to risk damaging the cells trying to pry off the tabs. I noticed some new part numbers recently without tabs, so my next board revision I'll probably put a coin cell holder there and start buying removables. – darron Jul 11 '12 at 17:23

9 Answers9

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6) The battery management logic and possibly some of the circuitry can be simpler and more effective if the exact battery type, and therefore the battery characteristics, are known. This could include getting more capacity out of the battery because the algorithm doesn't have to work accross a variety of battery characteristics.

Olin Lathrop
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  • Yeap, I observe the opposite with my Nokia phone. The initial battery was 800 mAh and charged fully in 1,5 hours, the replacement is 1020 mAh and charges fully in 2,5 hours - a whole hour longer with not that huge capacity increase. I'm pretty sure that's because the charging circuitry works suboptimally. – sharptooth Jul 11 '12 at 12:20
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    @sharptooth Or it's optimal with the original battery, and not for the replacement. – Random832 Jul 11 '12 at 17:30
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7) Legal dept recommends what the company should do with it's warranty claims, risk management to massive recalls, service costs and service profits.

If a user can service it with 3rd party batteries that fail due to mismatched energy management profiles or quality, it is a huge financial risk at every level from marketting, advertising, sales, service.

Was the design technology driven? No It is always about Revenue. And the sales of batteries is just a small part of the cost equation. The cost of failure from 3rd party batteries if they ever failed for any reason due to the host charger or even just the "loss of face " from media slander has a cost implication. AS well could Apple rely on consumers to re-cycle their batteries safely? They also have salvageable content.

Tony Stewart EE75
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8

5) The user can't replace the battery with the wrong type (especially voltage), which may damage/destroy the device. This could well be reason number one.

stevenvh
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Device design plays big part in this. Battery that is not removable is usually in very thin (less than millimeter) enclosure thus enabling thinner devices.

If same battery was to be made removable, they would need to add some rigidity to it and that usually means at least few millimeters increase in size.

Other reason is aesthetic one. Smooth lines seem to be favorable these days and, no matter how good your battery compartment is, external battery interrupts that smoothness.

Josip Medved
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The spring-loaded contacts commonly used for user-replaceable batteries have much higher resistance than other options, especially once an oxidation layer forms.

Ben Voigt
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    Although I have not seen the inside of an iPhone, I assume it also uses spring contacts since the Apple stores do have the ability to open the case (with a special tool) and replace the battery. But certainly there are other cases where the battery is soldered to the PCB and of course can't be easily replaced. – tcrosley May 07 '14 at 20:59
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Another reason I can think of is to avoid the need for a backup battery or supercap for the RTCC or memory chips that should retain data.

Bruno Ferreira
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I'm surprised nobody seems to have mentioned weather-proofing. Making a sealed case weather-proof (or waterproof) is fairly easy, but throw in a user-replaceable battery and associated battery door, and suddenly it becomes a lot more difficult to ensure that water cannot enter the part of the device where the electronics reside. Yes, it can be done (high-end cameras do it all the time), but is the buyer willing to pay the extra money for it?

Just one example of this: electric toothbrushes. Entry-level models can probably be manufactured for 10-20 dollars, if not less, and the better models likely don't cost much more in manufacturing. Now make the battery replaceable, add a battery door and the necessary adaptations to support these. The cost for this probably adds up to a fairly large fraction of that manufacturing cost, while delivering very little value to the customer.

user
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If the only time rechargeable batteries were swapped out when a brand-new nearly-fully-charged battery was replacing a dead one, and if after battery installation a unit would be allowed ample time to run a full discharge/recharge/gentle-top-off cycle before it was called upon to do anything else, then allowing user-replaceable rechargeable batteries might not be a particular problem. If rechargeable batteries can be easily swapped, however, users may expect that they should be able to batteries in and out with any state of charge, and immediately proceed to use them. This in turn will require that battery-management logic be bundled with the batteries such that it always travels with them.

If one could be certain that batteries would only be charged and discharged by devices made by the original manufacturer, bundling an inexpensive EEPROM with each battery would probably be sufficient. If, however, there is a possibility that batteries might be charged or discharged by a device which doesn't properly maintain the information in the EEPROM, behavior would likely be very poor. Including a charge-monitoring chip with the battery itself could avoid such difficulties, but would add significant additional expense.

supercat
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If the design treats the battery properly, most consumers will throw the device away before the battery needs replacing. You may still have your 1st gen iPod, but do you actually use it? And most devices are fine until they sit unused in a drawer, killing the battery.

gbarry
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