It's possible that the switch permanently disconnects because otherwise the voltage could creep up naturally as the battery isn't used (being loaded) and the disconnect would reset causing a load on the battery and a voltage drop and so it would disconnect again and repeat the process. 4 cells at 4.2 volt would be over 16 volts so a standard battery charger would not damage or over voltage the batteries in my opinion, though I would not recommend anyone to mess about with lithium batteries without proper knowledge, slightly too much voltage or to high charge current can permanently damage a cell or make it go up in flames violently.
What is the terminal voltage? Did the battery switch reconnect? Most Li batteries will not due to safety reasons.
It's possible that the switch permanently disconnects because otherwise the voltage could creep up naturally as the battery isn't used (being loaded) and the disconnect would reset causing a load on the battery and a voltage drop and so it would disconnect again and repeat the process. 4 cells at 4.2 volt would be over 16 volts so a standard battery charger would not damage or over voltage the batteries in my opinion, though I would not recommend anyone to mess about with lithium batteries without proper knowledge, slightly too much voltage or to high charge current can permanently damage a cell or make it go up in flames violently.
That is why you check your voltage first before the isolation switch, if you are over 14.4 volts you will not be charging the battery at all.