Here is some information on Roomba Battery
Maintenance and Troubleshooting tips that I gathered since I have been here, hope these help you:ROOMBA BATTERY MAINTENANCE
"Roomba's battery can last for hundreds of charging cycles with proper care. Here are some tips to extend the life of your battery, and help keep it at the peak of performance:
Frequent use - Rechargeable nickel-based batteries do best when used frequently. The worst thing for batteries like these is infrequent light use. The Roomba was designed to be used frequently; this will keep the battery healthy.
Keep the brushes clean - If the brushes and brush axles get clogged with hair and other debris, the unit will strain to spin them, consuming more power from the battery than normal, and battery life will suffer. In extreme cases, the battery can be damaged.
Occasionally exhaust the battery - At least once every week or two, make sure to run the unit until the battery is exhausted; it will stop running and will display a red light. It is not necessary to do this every time you use it.
Keep the battery charged - If you use the standard charger leave it plugged in all the time the unit is not being used. If you have a rapid charger, leave the battery in the rapid charger until just before you use it.
Buy a Rapid Charger and Second Battery - Using the optional Rapid Charger and a second battery will allow you to keep the unit running by swapping batteries between the Rapid Charger and the unit. In addition, the Rapid Charger's pulse-charging circuitry will optimize the battery's life while it waits in the Rapid Charger after completing its charge.
Keep the unit, batteries and chargers in a cool place - Battery life and charging efficiency are decreased if they are stored and charged in a very warm environment. They should be stored and charged in a cool dry place, out of direct sunlight and away from sources of heat such as windows, radiators, heating vents, and large appliances. Make sure the Rapid Charger and the unit have sufficient ventilation while charging. While it is charging a battery, the Rapid Charger should be sitting on a smooth hard surface (not on carpet or a rug) with plenty of space for ventilation.
Long-term storage - If you will not be using the unit for an extended period of time (more than a few weeks) it is best to fully charge the battery and then remove and store it separately. When you return, recharge the battery and then run it to exhaustion. The first few times you use it you may not get normal run times, but it will recover quickly if used regularly. Do not leave the battery in the unit for extended periods of time when not connected to a charger because it draws a slight current even when turned off. If left this way for more than a week the battery can run down. If left this way for many weeks, the battery can be damaged. Removing the battery from the unit will prevent this. Do not leave the battery sitting in the Rapid Charger with the Rapid Charger not plugged in to the wall.
If these tips do not resolve your problem, please contact customer support 877-855-8593."
In regards to the saving $$ on the VWU power, get rechargeable batteries instead. You can find 'D' sized NiMH at your local retail store.ROOMBA BATTERY TROUBLESHOOTING
I also recommend the following from iRobot's FAQ:
If you are having trouble charging Roomba's Battery, try the following:
1. Ensure that the battery is properly seated. Turn Roomba off, empty the Particle Bin, and place Roomba upside down on a flat, padded surface. Remove and re-insert the battery, pressing firmly on both ends of the battery until it clicks into place. Some batteries fit very tightly, and it is recommended that the end with the electrical connection be inserted first.
2. Make sure the battery is properly connected to Roomba and that the Charger AC adapter is plugged in to the wall outlet.
3. Charge Roomba overnight and run in the morning.
4. If using a Rapid Charger, make sure that the battery is seated correctly in the charger and that the Rapid Charger is fully plugged in to a working AC outlet.
5. If you are using a Rapid Charger in an unusually hot area such as near a heater or in direct sunlight, move the Rapid Charger to a hard surface in a cool, open area and recharge the Battery.
Your Roomba may be experiencing an issue where the battery is deeply discharged and may need to charge longer than the standard 3 hours. (or 7 hours if you have a standard charger)
Even with the charging light showing green (this indicates a fully charged battery) the robot is still charging. If your Roomba exhibits behavior where it charges for a short time then runs for a short time you will need to do the following.
1. Plug the charger into Roomba (if you have a home base be sure to plug directly into Roomba instead of using the home base, this will ensure the robot's charging cycle is not interrupted.)
2. After the Roomba's charging indicator goes to solid green please keep the Roomba on the charger for an additional 72 hours. (3 days)
3. After the 72 hours (3 days) has passed, turn your Roomba on and begin a normal cleaning cycle. If this works successfully it may take several uses for the battery to get back up to the performance it once had.
If this does not correct the problem, please call customer support at 877-855-8593 or e-mail us through our on-line form.
I have seen this with my refurbished Discovery and seemed to have solved the problem. Here is what they recommend :
"If your Roomba Red, Roomba (sage), Roomba Discovery, or Roomba Discovery SE is indicating a full charge, but it only runs for 15 minutes when you press clean, you need to reset the charging system. You can do this by removing the battery from the robot and unplugging the charger from the wall and robot. Please hold the power button down for 30 seconds. You then should charge the robot....."
Following this helped my battery from 45 minutes to 1 Hour 30 min. on hard surfaces. Let me know if this helped you!
Hope that these tips come in handy for all of you fellow Roomba lovers!
Nikolai - RobotReviews.com