I'm sure that is what you meant…but you also mentioned battery prices from $20 to $139. So the cheap $20 batteries needed to be commented on just as much as the $139 batteries.
Do you REALLY think that if the $20 batteries were just as good as the $139 Apple batteries…that ANYONE would buy a $139 Apple battery…heck no!!!
The truth is...the $20 batteries (for the most part) are cheap pieces of crap (depending who makes them & sells them)…and they could also present safety hazards. As I said above...some folks have reported decent experiences with them…and some have reported negative experiences.
If someone has an older 5-7 year old MacBook (that's only worth $200 bucks)…it certainly doesn't make sense to pay $139 for a new Apple battery…if the computer is only worth $200. So maybe someone in this situation rolls the dice with a $20-$30 battery.
If you want a recommendation for a decent replacement battery…check out OWC (macsales.com). They cost around $100. Less than Apple batteries…but not a TON less. Plus if you have a Unibody MacBook, MacBook Pro, or a MacBook Air…and you live near an Apple Store…the battery cost includes the installation of the battery (call it "free" battery install)!
HTH,
- Nick