if you have knowledge w/ basic electronics and computing mAh/volts, etc. you can diy it.. my laptop's standard battery lasts 2 hours (bnew) after few months 1hr nalng. repacked my batt and now it more than 3hrs.

ingat lang kasi high capacity battery means longer charging = overheat ng charger (baka masira//masunog esp if not airconditioned yung room - mainit) pero usually may mga temp protector naman mga charger so not to overcharge.