Hi Dom...If you have the 11.1v battery, then you can only use that battery size.
For a battery to charge, the charger needs to supply more voltage than what the battery is rated at, so it can "push" the voltage into the battery to fill it.
If the battery is 14v but the charger is only 11v then it won't be able to charge the battery to its full capacity, as once the 14v battery reaches 11v it won't have the required power to push past the 11v to charge the battery to 14v.
It will charge it but you will never get a full charge in the battery.
It all comes down to what the charger(or terminal voltage) in your laptop is.
Hope this helps explain the differences in the batteries....have only just joined this site as I had the same question and was researching the different batteries.
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