recharging batteries...

[Zebra]

textbook says you connect the battery's positive terminal to the positive terminal of the charger and the same for the negative terminals.... why is this the case? can someone explain

+

I dont understand why connecting oppositely charged terminals will damage the battery

thanks

[b^3]

To recharge the battery we need to force the electrons in the opposite direction. We do this by using the charger which will have a potential difference greater than that of the battery. So when we connect +ve to +ve and -ve to -ve, the potenital differences oppose and the larger rules over (i.e. the larger take the smaller) and forces the electrons in the direction it wants to go. This reverses the reactions and 'recharges' the cell.
I'm sure this part above is correct.
If you put +ve to -ve and -ve to +ve then what you are doing is adding the potential differences as they are in the same direction. You are speeding up the rate at which the charge is flowing through the cell and so making it go flat quicker, or other side reactions may occur damaging the battery.
I not entirely sure about this part, anyone else confirm, possibly Mao?

[Mao]

If you put +ve to -ve and -ve to +ve then what you are doing is adding the potential differences as they are in the same direction. You are speeding up the rate at which the charge is flowing through the cell and so making it go flat quicker, or other side reactions may occur damaging the battery.
I not entirely sure about this part, anyone else confirm, possibly Mao?

You are partially correct.

The power supply will force the reaction to go in 'discharge' mode. That is correct.

Discharging --> exothermic --> energy is released. In this case, since we're not connected to any external devices, this energy is released as thermal energy. (ever noticed batteries getting hot after use? same idea)

Power supply --> supplying energy --> energy of the system (i.e. the battery) gains energy --> the battery heats up. by a lot. because the wall socket can supply a lot of power.

The end result is both processes end up heating the battery. Which may end up melting it. Some of the chemicals inside the battery may vapourize, and eventually the pressure build-up may cause explosion. Or the battery may run out of reactants, and side reactions start happening, usually resulting in gaseous products and explosion.

(explosions are cool)