Nokia Battery pinout

Temperature is used in Li-Ion charging as a "qualifying" parameter only, not as an end-of-charge indicator. The charge regime used almost exclusively is current-limited constant voltage. After transition from CL to CV, charge is usually terminated when the current has tapered off to a pre-ordained level like

Unlike NiXX chemistries, Li-on and Li-Poly cells do not exhibit any sudden change in terminal characteristics as they approach "full charge", and they certainly DON'T generate any significant heat or exhibit any significant temp rise when charged correctly.

Yup.

I have designed a commercially available Li-Ion charger, and unfortunately they aren't cheap if they are any good. My client tested many available units before deciding to commission his own product, based on their unsuitability for one reason or another.

It is probably either of two items: a protection module connection or a temp sensor.

Temp is used as a charge "qualifier" (charging is inhibited if temp is too high/low).

Protection modules are normally employed in multi-cell packs. Their roles include over-voltage/under-voltage/over-current protection as well as monitoring and intervening in the event of cell voltage mismatch. The latter is necessary when a two-terminal approach is to be employed in charging/discharging a series string of cells, as otherwise cell voltage imbalance can cause individual cells to go under/over-voltage while the pack voltage is within spec. Because of the safety implications of this, protection is employed.

In a single-cell application (of which cellphones are the most typical), there is obviously no imablance issue so teh rpotection required is purely related to charge/discharge voltage and excess current situations. It makes sense - not always the driver of design/production though - to incorporate as much of this circuitry as is possible in the phone rather than the (disposable) cell. So I would not expect there to be too much of the protection system housed within the cell package. This is particularly so as the terminals on your 3315 type phone are fairly well protected from external contact when in the normal operating position.

Certainly thoughtful use of a DMM would reveal good clues as to the nature of anything connected to those extra terminals.

Most nokia's equipped with "Net Monitor" hidden menus are able to display a "temp" screen, which I believe is the reading from the batery module..

i found that on the blb2 batt is the two midde tabs tell the phone, the batt power levels and when to turn the phone off when the batt gets too low.to save the batt from harm.if your phone shows one bar left then bridge the two middle contact with tinfoil while in your phone then it will show "full power" and work for some time (good tip if your stuck somewhere with a flat batt).there is an unbeilveable amound of electronics for this inside the battery.there is a temp device inside but nothing to do with the 4 contacts it simply disconnects the minus connection from the terminal,(which looks like it should be the plus).

Thanks for that info. While these phones and batteries are very popular, there seems to be little in the way of technical info available for the battery.