We had a call from a customer wanting to know why there are so many lithium battery contacts on phones. “Your lead-acid batteries have only two terminals and they work a treat,” they explained. Moreover your blog posts only speak of two electrodes, namely a cathode and an anode. This difference made us curious.
The Number of Lithium Battery Contacts Depends on the Device
When we removed a smartphone battery at the office, we noticed it had three contacts. We hadn’t looked at phone batteries that carefully before for this fact to sink in. When we investigated, we discovered only two smartphone lithium battery contacts are for power supply.
The third ones are there because lithium cells can be unpredictable in terms of available capacity. Therefore, the third contact is there to monitor the “usage” chip. This in turn observes the charging / discharging cycle to provide a more accurate report of remaining capacity. Then we discovered these usage chips sometimes get confused. This is why occasional full charges and discharges are necessary to reset lithium battery limits.
So Far So Good, But Why Does a Laptop Battery Have Even More?
“That’s all fine and dandy,” a precocious young member of our team asked. “But why does my laptop have more than three lithium battery contacts?” We need people like that to keep us on our toes.
We realized, after a brief office think tank that smartphone batteries are single cells. Whereas laptop batteries comprise multiple cells necessary to build enough volts. Therefore, we have to monitor each cell individually during charging, just in case one starts giving problems.
Only high-end phone and laptop batteries have sufficient intelligence to monitor the conditions we mentioned. This is why manufacturers recommend only replacing like for like. During our research we discovered some low-end batteries have dummy sensors. These may report ‘all is good’ regardless of what is going on inside the battery.
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Preview Image: Blackberry Phone and Two Pin Charger
