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Comment by wodenokoto | Hacker News Reader

I've noticed that battery life changes dramatically on where you are. When I visited the US, I bought a local SIM card and my 4S died long before the day was over. The same in Japan. But in Denmark I have no problem lasting a day.

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Yes, this definitely happens. I live in Australia and have gone out to north-west Queensland many a time, when you do your battery life is halved compared to being in the city. You'll even find the same thing catching a train from Gold Coast to Brisbane. Basically, anywhere there is spotty coverage, you'll see your battery life drop dramatically, this is because the phone will increase power to the cell radio to keep you connected when there is low signal. I've always found it fascinating.

Back in the dumb phone days, driving through New Jersey, of all places, used to kill my battery. If you're not familiar, NJ is the most densely populated state in the US, but the northwest part of the state is mostly wooded, fairly mountainous, and sparsely populated.

I'd be driving from Pennsylvania the NYC suburbs, but northwest Jersey at the time had spotty service and a lot of analog networks. It was a real battery killer.

Thats an interesting observation, and is line with what I have seen.

We develop various GSM products, and I have noticed network packets delivered to our products at various times of the day, different for each GSM network. On one network it was every morning 08:00 a packet would be sent from the network to our device. (I could see it by seeing the modem would exit it's low power mode). I have not yet tried to do a capture of the packet, as it might be something destined for the modem baseband or sim card.

Anybody care to venture a guess? Perhaps a network ping or something?

GSM networks ping all devices on regular intervals (besides the handoffs between cells when traveling and when there is data to transmit). This interval is a setting of your network, from minutes to hours.

Thanks PanMan,

I suspected something like this.

I've noticed the same. I get the impression that the stronger the network signal, the better the battery lasts - I assume because the radio has to increase the power with which it communicates with the tower when the signal is weak.

Correct, the GSM modem do indeed vary its transmission power depending on the RSSI (received signal strength). Also with low signal strength packets get dropped, so needs to be retransmitted, which also drains the battery more.

This is interesting, do you have any resource on this topic?

I wonder how a phone with dual sim can handle battery life? Thats totally an interesting problem to solve. I use micromax which is a dual sim and the battery life is pretty good, last for a day.

Which may account for the wild variance in reported battery life from different people with the same model of phone.

Can verify this. I was working for a client who was located in an area that had maybe 1 or 2 bars of LTE service - my phone was below 20% at the end of the day if I didn't charge it. Now that I'm in a big building with AT&T microcells, I get 5 bars LTE so my phone is at over 50% by the end of the work day.

Yep, and it's very obvious even in different parts of the city for me. In one office, the phone is still at 60-70% after a day's work, while in another it's usually dead by the end of the work day.

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