When buying a tablet always for one that can give you at least 8-10 hours of power. Otherwise, you always be running around from plug point to plug point in search of it. Read the tablet specifications to understand its rated backup.
- 2600-4000 mAH: Tablet with a battery of 2600-4000 mAH gives a backup of up to 4 hours
- 4200-5600 mAH: Tablet with a battery of 4200-5600 mAH gives a backup of up to 8 hours
- 6000 mAH & above: Tablet with a battery of 6000 plus mAH gives a backup of more than 8 hours
Other than this, there are some tablets which come with a detachable keyboard that also has an extra battery in the keyboard case. This can improve your battery backup by a significant margin. Another fact to remember is that Li-Poly Batteries provide a higher back than Li-ion batteries.