Battery Health decreased to 86% after full discharge and charge(Calibration).

I am an active user of my Macbook Pro and am into the habit of using it plugged in most of the time.
My MBP is early 2007 model, is 6 months old and has done 31 charge cycles (out of which 3-4 must be full discharge whereas most others would be partial like use from 95% till 30-40% battery charge is left and then charge again). I also play games under windows xp on my mac for considerable time (for 5-6 hours each Saturday and Sunday) with charger plugged in all the time.

My Battery Health has suddenly dipped to 86% after the previous calibration process(full discharge and then full charge). It was about 94% prior to this calibration process.

I want to know how bad is this 86% battery health?? Should I get it replaced immediately or could it be that it is a temporary error.
I use iStat Pro for battery monitoring.

Please provide suggestions why this could have happened as I take pretty good care of battery.

Would Apple provide free replacement as MBP is still under warranty?

Mine slowley started to climb back up it was down to 91%,then went back up to 99%

Give the battery some time to come back up to 100% charge. If it doesn't, you may have to do a deep discharge cycle first. Leave the machine on overnight with the power saver settings turned off - all except for the display. When the battery falls below where it can sustain memory, the machine will sleep. Recharge and see what happens.

If your battery turns out to be defective and the machine is still under warranty, Apple will replace it.

Regards.

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I decided to try the full discharge and charge again.
Just when the charge was 10% and a battery warning popped up, I happened to check the battery health and it was back again to 94%.

Then after draining the battery completely, I plugged in the power and left it ON till morning.
Will update soon as I Didnt have enough time to start the notebook to check Battey Health in morning after full charge, but hope it does not go down again.

One time mine dropped from 84% down to 32% after discharging and recharging, I called apple about it and they sent me a new one.