Schneier on Security

Clive Robinson • March 3, 2014 5:05 PM

Hmmm,

I don’t know when this bit of kit was designed but the photo of it looks like a 1950’s “battle ship radio”… I suspect it may be using a modified old style TEMPEST case.

Appart from the Geolocate and 3F comments there is little or nothing to go on as to it’s capabilities, and with what USD I would be expecting one truck load of capabilities (including esspresso machine and kitchen sink 😉

Clive Robinson • March 4, 2014 4:08 PM

@ Terry Cloth,

SA: My laptop battery reads “NOM 10.8V 5.2AH”. Can I presume that means VxAH=56 WH?

No… but it is safe to assume the lie it’s telling you is in part true.

Long story short rechargable batteries have odd properties as well as internal resistance. It is only practical to read the overal voltage of the cells (which are usually series connected). This voltage varies with load and temprature both ambient and inside the individual cells. Temprature criticaly effects just how much energy you can pull back from the cells and over what period (as energy in time gives power this makes calculations difficult). Thus in your laptop somewher (possibly in the battery) there is software with a “lookup table” that as a minimum takes total cell voltage as it’s input and amp hours as it’s ouput and it is at best an aproximation based on tests carried out at some point in the past to make a model of average performance.

Some batteries have their own little microcontrolers monitoring the battery cells load, tempratures, number of charge cycles and if they were full or partial, the battery age etc. This can dynamicaly update the look up table and also talk to the charging circuit in the laptop, all to wring the last little drops out of the battery performance.

Of course such a system is open to abuse by the manufactures or “in the know” attackers and thus could harbour malware etc. Or cause you to not be able to use third party batteries –even though such practices are probably illegal in Europe– the profit in doing so is to tempting to pass up for most manufactures who often talk about warrenty liabilities to evade further enquires from authorities.