I have heard that keeping the battery in, all the time, when the system is plugged in ruins the battery. So I took the battery out, and went I put it back in, it was completely dead, and would not hold a charge. The guy at the battery store told me that if a battery's charge goes completely out, the battery may no longer be able to be charged.
So damned if I do, damned if I don't?
I have also heard that if I charge a batter too soon, the battery will "remember" where it was before I charged it, and will consider itself uncharged at that point. For example, if I charge a battery when the battery has 50% of it's charge left, then for the remaining life of that battery, the battery will need to be recharged when it hits that 50% mark. So what happens if the charger is removed for a moment? Does that mean the battery will need to be recharged once it has run down 1%?
Any advice on how best to maintain my laptop battery?
You forgot to mention, is this a Li-ion or NiCd battery
For the OLD ni-cad batterries, you are correct about memory. For these batteries you should discharge complettly before charging (complete discharge is when Battery voltage equals 1 volt Per cell, ie a 10 cell battery, Eout equals 10volt when discharged, and 12.5 V when fully charged- CAUTION do NOT let these batteries drop below 1 volt/cell.
Ni metal Hydroxide simular to NiCd, but less of a memory problem, same charge and discharge as above.
Most laptops (past several years) us the Newer Li-ion Battery. These DO NOT have the memorry problem and you do NOT need to let them discharge completely. For one of my laptops I have two batterries. What I do leave one battery in for 2 weeks to a Month, then swap batteries. You can leave the battery in or leave it out - but put back in at least every 2-3 wks and top up the charge. My second laptop I just leave it in.
My Old Laptop (5 yrs or more old) use the old NiCd batteries which I remove when not in use and periodically put in, run battery down until it says low batterry then I recharge - DO NOT do this for Li-ion batteries.
Unfortunately big brand laptop manuals are a bit weak on any instructions here .... My laptop came with detailed instructions and explanations covering both battery technology and charging technology. The manual's recommendation is to do whatever ya normally do with the laptop w/o worrying about the battery. Once a month, let it discharge completely overnight and charge it in the morning. I do this once a quarter and battery life on our laptops is about 95% of what it was when they were purchased....oldest is 4+ years.
This discharge by the way is not for the battery .... it's for the charging system. The charging system logic generally moderates the voltage applied starting with a higher voltage and tapering off as battery nears full charge. By discharging the battery, the charging system recalibrates the span from dead to full. This prevents the charging system from applying incorrect voltages where it should be in the "tapering off" mode.