Can you recharge batteries if they're not dead yet?

Okay can you like recharge the rechargeable batteries when you didn't use all the juice up? Is it bad if you recharge it when you didn't use all the juice?

Truth is, rechargeable batteries can only be charged a certain amount of times before they just don't work anymore. I don't know how many charges, I'm sure it varies with each brand. But I give mine quick charges all the time and I've had them for 2 years, so I am sure you can keep charging them for a while. =]

We used to put dead batteries in the oven for a while. That seemed to give them a bit more life. I have seen things for sale that claim to recharge ordinary batteries but an electrician friend told me they don't work.