Using rechargeable batteries saves loads of energy, waste (including toxic chemicals) and money.
A typical standard AA battery can be bought for about 20 cent (€) when bought in large packs or discounts. A standard rechargeable AA battery costs about €1 but can be recharged up to 1,000 times. Even accounting for some degradation in the battery (say half), the up front costs, ignoring the waste disposal costs, are €99 per battery! Pure and simple!
If you have 10 batteries in your home, that is a €1,000 saving over the life of the battery. Now see if a bank/investment will give you a return like that.