Laptop batteries are supposed to go through a charge/discharge cycle. If you are using the laptop with AC adapter plugged in all the time, it is charging the battery all the time. This will shorten the battery life. If this is your case, remove the battery and put is some place that is dry.
I understand your point but if a new battery only gives half of what it should be delivering then is it the battery or the charging circuitry, given that it is happening with two new batteries? What you are saying should show itself after some time, not in the beginning. Am I reading you correctly?