One advantage a 1.5 v rechargeable battery has over a 1.5 v disposable battery is that.

1.5 V batteries are typically Alkaline-manganese and/or carbon zinc which have a native open circuit voltage of 1.5 volts. But during discharge they will drop to lower voltage levels due to becoming depleted and internal resistance to current flow. Knowing this, virtually all battery powered devices are designed to be able to work with depleting batteries down to 1.1, 1.0 or even 0.9 volts per cell.

"the day we found the sharks' teeth" i would say highlight the element of the plot as it sets its boundaries and centers the adventures of them being on a boat and cleaning spit of sand.

c, his tragic flaw to cause his downfall