Replacing PRAM Battery in iBook G4

An Apple retailer played with it and said my old iBook (info below) needs a new PRAM battery.

--It is 2nd-hand to me so I don't know its history.

Machine Name: iBook G4

Machine Model: PowerBook6,7

CPU Type: PowerPC G4 (1.5)

CPU Speed: 1.42 GHz

Bus Speed: 142 MHz

Boot ROM Version: 4.9.3f0

Serial Number: 4H602350SE9

The Apple retailer said it would cost about $150 to replace the PRAM battery because it is so hard to get to.

But when I search online, some people say there is no PRAM battery at all, or that it is within the main battery's sealed case.

--BTW, my main battery holds a good charge, but I don't know this battery's or this laptop's history.

I would like to know what I am faced with here.

--Is there an actual PRAM battery for this particular laptop?

--Is there an online "How-To" to find and replace this PRAM battery?

--Do I have to replace the main battery to get a new PRAM battery?