OK, as a dive computer designer who has done both disposable and rechargeable designs (Atomic's Cobalt), I'm in a position to address this. I'll use Cobalt as an example, but allowing for design variations the comments are applicable to other computers. Bottom line: all designs are tradeoffs between competing requirements- legibility vs. small size, bright, clear display vs. power consumption, etc. There is no one right answer.
Most things in the article (it's not really technical, it's marketing) are "true" in the strictly literal sense, but there is significant spin and the story is incomplete. I expect it's designed as a sales response to questions like "how come you don't have color screens, or rechargeable batteries?" As such it's more than a bit misleading.
Monochrome LCD displays like Cochran (and most other dive computer manufacturers) use do have very low power requirements- in particular, they don't require much current at any one time, which means they can use compact "coin" type cells that are incapable of delivering much peak current. That is in fact a huge advantage if you want to make something wristwatch sized.
However, the statement that OLED (specifically AMOLED) displays have "extremely high power requirements" is just wrong, at least compared to other high resolution color displays. We chose the AMOLED display for the Cobalt in large part because whenever pixels are off they use zero power, so we could design power efficiency into the product. Modern TFT displays with high efficiency LED backlighting are now just about as good, though. Both of these display technologies use far more power than a monochrome LCD display- at least until you turn on the backlighting. Whether the greater readability of a relatively large, high resolution color display is worth it to a diver is just an individual decision. Point by point:
"Exploding batteries"
A bit of hype- this is (and the referenced recall was) typically a problem of bad chargers, rather than batteries. We actively tried to get the Cobalt's Li-Ion batteries to explode, burn, or otherwise misbehave, including with severe physical damage and saltwater, dead shorts, etc. and we couldn't do it. Worst case was a kind of weak fizzle.
"Sudden Shutdown"
It's true that rechargeable batteries have a steeper power curve, rather than a gradual decline. That means they need to use a "fuel gauge" designed for and calibrated to the battery type. This is true of every cell phone and modern electronic device using rechargeables, these parts are readily available and work well- this is a non issue. A full charge on the Cobalt's battery will last typically 40-60 hours of diving, and six months of standby. We start warning to charge when the level reaches 20%, or about 10 hours of active diving time. Charging takes about 2 hours and can be through USB (including solar or car charger) or a wall charger. It just has not been a problem.
"Finite Recharge Half-life"
The typical LiIon batteries we use in the Cobalt are rated at 5-700 charge/ discharge cycles before losing significant capacity- that's about 20,000 to 40,000 hours of diving. So while technically true, this is not much of an issue.
"User Replaceable"
Most computers I am aware of now using rechargeables are user replaceable- maybe I'm missing something. Cobalt is user replaceable if it ever were to become necessary, but we would prefer the diver go to a dealer, as the battery is not available off the shelf. It doesn't need to go back to the factory. However the battery charges without removal , and we expect that for the vast majority of users the original battery will last the life of the computer, so it's a non-issue in almost every case.
"Self Discharge"
Again, true- rechargeables self discharge. For Li Ion this is a couple of % per month, which translates into years of shelf life before needing recharging. Long storage life is one of the strengths of the Li-Ion technology. In practice, our battery will run down in about six months, not from internal discharge, but because every few minutes the computer samples ambient pressure. This is so if you jump into a mountain lake without turning on the computer first, it uses a correct ambient pressure for deco calculations.
"Zero-charge life", "Over Charge Life"
True- rechargeables shouldn't be totally discharged or overcharged. Any device using rechargeables should know to shut down or stop charging before the internal charge reaches the point where there is any risk of this. Actually it will start a slow trickle charge cycle for the last phase of charging, then maintain or shut off, depending on what it sees. The battery in the Cobalt won't be damaged by being left on the charger. The Cobalt also won't allow the battery to discharge below the minimum recommended voltage, and contains a sophisticated chip to monitor the pace and rate of charging so as to optimize battery life and performance. I expect other computers using in situ charging are similar. This is just normal design, as is used in millions of consumer products.
"Long Term Storage Life, Degradation"
It's true optimal storage life occurs in a partially charged state, but we are not talking about huge differences here. Since the Cobalt's battery is always "in use", even in storage, it becomes a moot point. Degradation? Their source says LiIon batteries "ail become inoperable after two or three years"- I'd have to call that just wrong, I have probably 50 batteries for Cobalts that have been around here for five years or more, and are still going strong, and I could say the same for a number of other devices using rechargeables. All batteries- disposable and rechargeable- have a shelf life, and long shelf life is one of the strengths of the Li-Ion technology.
"High Initial Parts Cost"
Absolutely true. If you want rechargeable batteries, or color screens, or high resolution, you are using much more expensive parts and it will cost more. Again, that's a decision for the diver to make, and why there are different designs and price points.
"Replacement Battery and Related Cost"
This comment puzzles me- it's correct that battery cost is minimal for either type, but they mention factory battery replacement of rechargeables as a high cost factor- I'm not aware of any dive computers using rechargeables that require factory battery replacement. AGain, maybe I'm missing something.
"Bulky Charger"
We designed the Cobalt with the ideal of being able to take a week long live aboard trip without charging. In practice, particularly since all you need in order to charge is a small adapter and a standard USB cable, it has been a non-issue. And solar, car, laptops, etc. all work as power sources. Planning might be necessary on a very long or remote trip, but the same would be true for disposables- the real difference is from having a high resolution color screen- that is going to require either more batteries or a charger on a long trip.
"Relative Reliability"
It's certainly true in the abstract that more complex systems tend to be less reliable, and rechargeable systems are more complex. But in practice, with millions of consumer products in daily use, rechargeable systems are highly reliable, if well designed.
"Battery, Fuel Gauge, Coulomb Counter, and Warnings"
They are correct in that a properly designed fuel gauge and firmware must consider these factors- temperature, battery state, use, etc. We do, and so, I expect , do most of the millions of other rechargeable products out there. It's actually a bigger problem to know about various kinds of disposable batteries that can be found in standard format sizes- it's possible to find AA sized batteries, for instance, with wildly differing characteristics, and charge monitors may have no way of knowing what is installed.
"Planned Obsolescence"
This seems a straw man argument. Are there any dive computers using rechargeables that don't allow for battery replacement? Not that I know of. They say "On a rechargeable system with a user replaceable battery, if the battery life is too short then the diver may need to carry a number of spare batteries to last a full week of diving
" Since we deliver a week or more of diving on one charge, and 20,000 hours or more on one battery, this comment seems disconnected from reality.
My opinion: This is a lot more about display technology and design than about batteries. Low power, monochrome LCD displays use very little power- almost none. But if you go to a higher resolution display, whether backlit like TFT or emissive like AMOLED, and particularly using color, you need more power. That can be either disposable batteries, like the Shearwater Petrel (which can also use rechargeables), or a rechargeable battery that charges in situ, like the Cobalt. But it will end up being a bigger battery or having a shorter life between changes/ charging, or both. The high resolution color display will also be more expensive- by a lot- requires far more development re. the interface, and generally it will be a more high end and expensive product. Those are tradeoffs for better legibility, particularly in dark conditions, and a more sophisticated, easier to understand interface. The current state of technology is such that we can't provide a high resolution, color dive computer that is lit for excellent visibility, costs $3-400, and runs for years off of a disposable battery. But that's why we have a variety of products- to meet a variety of needs. It's not necessary to trash one approach to validate your own.
Ron
