Thursday, 2 July 2009

Li-Ion battery management

Colin Jago had a post recently in response to Panasonic's decision to restrict camera battery use to on-brand only through firmware updates. It seems all their firmware updates are getting the treatment. I realised that the opinions (mine included) seemed rather ill-informed conjecture. So off I went to investigate the whole Li-ion thing, this post is the result.

I had two mind beginning this: the cynic in me regarded the Panasonic decision as pure marketing wrapped in a dodgy safety message, the engineer in me wanted to understand the risk and whether I was actually placing myself in harm's way.

I've included some handy references at the end rather than pepper this thing with links. I read a bunch of stuff, the links provided give all the information in a handy to digest form. Of course, you will have to make up your own mind, I cannot be responsible for your actions and I'm not advising anyone to follow my lead. Caveat lector.

Side-bar: testing batteries
Scott Kirkpatrick provided this link to some testing of Olympus batteries which highlights some of the problems. What do these tests show? First that there are products out there that do not have the protections built-in that they should have. Also, that there appear to be many products using common components (partly supporting my theory of limited manufacturers).
What these tests do not show (in any way, as they didn't try) is that the OEM or high-end third party products are any better. By not dismantling the Olympus product they don't support the premise Panasonic is working under that their products are inherently better. There is also no evidence that any particular manufacturer provides a consistently reliable (or unreliable) product, these being single sample tests.

As I see it, there are 4 parts of battery care: charging, handling, storage, device design/usage

There's not a lot a user can do about the last of these, that's just the kit you use. So what about the rest?

Charging - One of the sources of risk in using Li-Ion batteries comes from the battery being over-charged. There are 2 ways this is controlled, through a charging algorithm in the charger which limits the voltage and current during the charge cycle and shuts down the charger when it's done. The second part is an over-voltage protection circuit in the battery should the charger not provide the protection or fail. Both need to fail or be absent to present a failure mechanism.
Handling - carrying, inserting etc. Most batteries have mechanical control to prevent wrong insertion (i.e. the shape of the battery and compartment must match with only one orientation allowed). In order to prevent dangerous failures of the battery out of the equipment, it should be prevented from short-circuit (which seems to present more of a risk than older types due to the internal chemistry) and protection from overheating. Again, batteries should have protection circuits for both of these problems. The US Department of Transport (DoT) rules on carrying batteries in luggage are aimed at minimising the risk of short-circuit by enforcing a carrying method that specifically stops it happening.
Storage - Similar to handling, batteries should be kept from overheating and short-circuit. There is another aspect and that is battery life. The life of Li-Ion batteries is greatly extended by storing them at less than full charge (40% seems typical advice) and at lower temperatures (e.g. refrigerated but not below 0degC).

Low-quality, no-name batteries are more likely to have poor protection circuits which means you are relying more on the charger and device to prevent problems, which increases the risk by increasing the probability of an event happening. The consequences are the same, however.
Side-bar: Panasonic and the Law of Unintended Consequences
I don't know exactly how Panasonic enforces the restriction but i presume it is some sort of electronic tag in the control circuit. Maybe they'll license it to respected manufacturers, maybe not. even if they don't, I expect a bunch of unscrupulous companies to clone their batteries. Likely the sorts of companies that don't include proper protection in their products today and spoof the exterior packaging too. If the technology isn't licensed, then the chance of poor third party products being used goes up as there aren't the reputable ones around. So the problem doesn't go away.

For Li-ion batteries they should have control circuits with over-voltage protection, over-heat protection and short-circuit protection to help minimise the risks from poor handling or usage. It does not eliminate all the risks. But then that is not unique to this particular power source (remember the old, leaky zinc-carbon batteries?).

There is an aspect that I've not talked about, and that is internal failure of the battery. The large laptop battery recall a couple of years ago highlighted this. While the chargers, devices and batteries all had the correct protection circuits all failures came from internal manufacturing defects that were not protected by the circuits. The actual number of failures was low, maybe partly determined by usage pattern as inherent risk. That's easily the biggest case of Li-ion battery dangerous failure and it had little (if anything) to do with usage.

My conclusions: It appears that Panasonic aren't guaranteeing a camera's power usage control, by implicitly requiring the protection circuits in he battery itself. They can't guarantee which charger is used, regardless of battery used, so I presume expect their batteries to provide the protection. The actual chance of failure, regardless of battery type, seems very low indeed. So the decision does not, to me, represent an appropriate response to the risk, they could just as easily have issued an indemnification as part of their warranty. Then there is Law of Unintended Consequences (see sidebar). So, to my mind, this is pure marketing wrapped in a thin safety veneer.

Risks come from: poor charging, easily controlled by using quality product. Short circuit controlled by handling regime (US DoT response is a good, risk-based approach in this regard), poor device control and there we're in the hands of the manufacturer.

My regime: I buy branded non-OEM batteries. They are cheaper but should still be good quality. I avoid the low-quality, bargain priced units. I carry and store them in a protective case and will like now store them in my refrigerator (alongside all that film).

Some links:
Good place to start is (as ever) Wikipedia.
There is a lot of information at Battery University, not just on Li-ion. Specifically they have information on Li technologies, usage and safety. There is also this nice article on Li-ion battery chargers, which explains the best how they work.


  1. It would seem that not even OEMs can always guarantee quality either:

    There's a thread on the issue you raise at DPI Forum. I also use 3rd party batteries without any problems.

    Now if you want to really frighten yourself look on Ebay for Lithium Ion Liquid Polymer cells ~ a battery cell in a plastic bag!

  2. Indeed, which is why I mentioned the laptop recall. I found quite a few other examples (the linke Wiki article has several).
    So far as I can tell, all the recalls have been due to unprotectable manufacturing faults. And I bet all the "OEM" batteries are actually manufactured by 3rd parties, several at that for larger brands.


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