Gordon,?
Good point, the two big spring loaded terminals, (which mostly have 4mm sockets set in them) are the positive and negative battery connection, and the two smaller, flat contacts connect to thermal cut out switch/s, and sometimes a PTC resistor inside the battery pack, that tells the various different chargers how to charge the battery, or if it is deemed fully charged, etc. ?
Other then those components, the battery is not usually ¡°smart¡±, so if charging it via the audio connectors, you need to make sure the charger you¡¯re using, or PSU, is current, voltage and time limited, otherwise it will eventually cook the battery, if much over 45mA.
One of the small flat connections often also connects to a battery terminal, so worth checking inside a battery first, if it¡¯s newly acquired, to make sure. ?They¡¯re very user-friendly batteries for rebuilding, either to donate their original innards to build something else, or to fit lithium batteries in, with suitable charge controllers and BMS circuitry.
73
Al
G8LIT
