Phones caching battery status on SIM?

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B. Wright - 24 Jul 2006 14:10 GMT

Just curious, does anyone know if some GSM phones cache the
battery status (i.e. remaining charge) somewhere in the SIM then
retrieve it later if the phone is power cycled? I noticed the other day
when swapping to a different SIM temporarily that the battery meter went
from nearly full to nearly empty, then when the other SIM was put back
in the battery meter went back to where it had been previously. The
battery definitely was not even close to being discharged, this is what
makes me think the phone cached/read the status from the other card.
A bit strange, but that's the only explaination that seems to make
sense.

What other items are cached/udpated regularly in the SIM? I've
also noticed on a SIM swap the initial power on takes quite a bit longer
than usual too and it seems to be reading/writing the SIM for quite a
while (no access to numbers stored there until it's done).

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Me - 24 Jul 2006 18:22 GMT

> Just curious, does anyone know if some GSM phones cache the
> battery status (i.e. remaining charge) somewhere in the SIM then
[quoted text clipped - 11 lines]
> than usual too and it seems to be reading/writing the SIM for quite a
> while (no access to numbers stored there until it's done).

If you read the SIM specs, you'll find out that there is no memory
standardised for storing battery info, I don't either see why any phone
manufacturer would want to do that. If you observe different battery
capacity indication just after switch on, for two different SIM-cards, for
the same phone and battery (battery not charged, neither used more than
necessary for power up), I would guess that being either random measurement
error at the phone or an old battery and registering to a different network
on a distant cell tower could use more power and make the batter go a bit
flat, or something similar.

The phone does store information about the local cells to the network, to
speed up service at next switch on. Most phones store this, and more
accurate info to the phone itself and use this info instead of that from the
SIM (the SIM info is optional for the mobile anyway). This only affects the
time to get registered to the network, not the time to have access to SIM
phone numbers.

The time it takes for the phone to access SIM phone numbers should be mainly
SIM dependent (age/interface speed, memory size etc.), a bit perhaps mobile
brand/type specific. But I assume you were referring to an experience with
the same phone device and with different SIM cards.

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