The cheap batteries usually do not affect the computer badly in anyway, and when getting a replacement one or one to switch out to (if you like carrying extra batteries on you) they (assuming you get them from a good source) will last the computer the same length of work-life at half or such the cost. Laptop batteries are not just larger cells, placed in sequence. They are usually provided with some sort of small board that regulates the charging rates and distribution of power on a basic scale. The computer can read the little pcb board in the package and ell maybe using a simple resistor current testing or some small handshake. However, not to worry, this should probably not affect your choice of laptop because the warning can be turned off and the battery can be replaced with a real one for maybe $30-40 which is effectively a small cost to pay to replace anything on a laptop. Windows will get a battery is almost dead message showing up if they sense the battery life is failing, even with most cheapo brands. Anyhow, I've always found that buying a cheapo whenever needed always worked me out the same as buying the "real one". Cheapo brands can come with the lying about capacity disadvantage but you can usually resolve this by buying a higher capacity cheapo pack or testing it yourself with discharging rates in the computer. The Chinese knock-off will also be relatively easy to tell when removed from the back, usually by particularly shoddy labeling looking nothing like the real one (look online for specific pictures).
