I see absolutely no problems with getting a battery with a higher capacity so long that the combined cells equal the same voltage as the originals.
Those of you that have said otherwise, care to post a link or three as to why this shouldn't be done?
no links, just general caution. [edit: see below, links now included.. dont go too crazy in choosing larger capacity replacements
I would rather err on the side of caution rather than take a chance of a charging circuit overheating. get a battery that needs twice the charge, the circuit works twice as long. is that OK (after all it charges for hours at a time anyway)? probably and I personally would do (and have done) it but Im sure not going make a blanket statement and tell someone else its absolutely fine to do it and chance ruining his laptop. I dont know his laptop and will not risk telling someone to go ahead and put a pack in there that is rated beyond what a manufacturer offered and qualified for that machine. [edit see links below - stay within manufacturer supported capacities
if you feel comfortable recommending it, fine. Ive even done it myself (get the largest capacity I could find) but I just dont feel comfortable telling someone else that. not my hardware to risk, however small that risk may be.
EDIT: avanish, if you replace the batteries with larger capacity ones, your run and charge time may be off till it completes several charge/discharge cycles to recalibrate.
EDIT 2: here are 2 links on rapid charging nimh batteries. seems if you go TOO far in using larger capacity batteries (like 2x or more) you actually can do harm in some situations like rapid charging (which is charging between .5C and 1C.. double the capacity of a pack that charged at .7c and its now charging at .35c, below the fast charge rate but well above the trickle charge rate) . depending on how the charging circuit operates, you can fool the charger into over charging the battery (and maybe venting it big time) if it uses temps to figure when to switch to trickle charge mode as the temp rise may not be high enough or fast enough to trigger the switchover. same principle applies in voltage monitoring for the switchover, at rates below .3C the voltage swing may not be fast enough or high enough to trigger the switch as it expects fast charge rates to be .5C-1C
those temp and voltage changes only happen as expected at a specific battery charge rate (in relation to capacity, IE .5C - 1C), go outside of that rate and the temp and voltage swings that the charging circuit monitors will not be what it expects and it can overcharge the pack.
since none of us know the laptops charging rate with a manufacturers largest capacity pack we cant say how much bigger you can safely go. if its 1C you could almost double it, if its .6C then even a slight increase in the capacity beyond what the largest capacity the manufactured offered will screw the charging circuit up.
also, keep in mind there may be a chip in the pack that tells the computer what capacity the batteries are and it bases its charge on that. replace the batteries and the capacity no longer matches what the packs chip says.
panasonics take on charging nimh
and duracells take
Ive never gone over twice the capacity in any of my pack replacements (simply because Ive never found any that offer twice the capacity and still fit in a given project) so Ive never run into this.
it all depends on the charging circuit. as I said before, since its not mine, and you know the laptops charging circuit is rated (and calibrated for) capacities that the manufacturer offered, stick with what they offered capacity wise. its the safest thing.
sorry for the long winded reply, but you asked