Is it my Roomba or my battery ?

Is it my Battery or my Roomba


So your last battery just wouldn’t  run your Roomba anymore and you bought a new battery for it.  You install it into your Roomba the battery status pulses amber for awhile and then goes green.  You send the Roomba on a cleaning mission and it runs for about 1 to 5 minutes before the status goes red and it stops.


Using the pictures and description on this page will help you determine whether your Roomba charging system or the battery is defective.


There is another thread on this website that you can go to that will help you determine if the battery can provide the needed power to run your Roomba.  It’s in the “How Do I” section. 


This page will help determine if the battery will accept a charge by using your stock Roomba power supply connected directly to the battery using some electrical wire. The power supply being used is the standard black iRobot power supply.  Make sure at this point that the power supply is NOT plugged into an AC Outlet.


You can obtain some short lengths of wire ( about 4 inches or so).   I use Red for the positive connection and Black for the negative connection.  Strip the insulation (about ½ inch) from both ends of both wires.  On the Red wire fold one end of the un-insulated wire back on itself so that when it is inserted into the barrel of the power supply it will fit tightly and not fall out.   Insert the other end of the Red wire into the farthest connector from the body of the battery.  Strip enough insulation from one end of the Black wire so that you can wrap it around the outside metal portion of the barrel of the power jack, insert the other end of the Black wire into the battery connector closest to the battery body.


When the final connection of the Black wire is made, you may observe that the LED on the power supply is on.  This is normal if there is some battery voltage stored in the battery.  Now, plug the power supply AC cord into an outlet and let it charge the battery for no more than 10 minutes.  Do not leave the charger connected for longer than 10 minutes and don’t leave your charging scenario unattended.  After 10 minutes, disconnect the charger from the AC outlet and the battery.  Install the battery into your Roomba and see how long it runs.  If the run time is longer than when you first tested your battery then the battery is OK but there is an issue with the Roomba charging system.  On the 4XXX model Roombas there is a well know charging system hardware fault that occurs sometimes when a defective or very low voltage battery is inserted into a Roomba for charging.  More charging current is consumed by the system than it was designed for and this then causes one or both MOSFETs (U2 and U4) to cook themselves internally and fail.  The only resolve now is to either get out your soldering iron and replace U2 and U4 MOSFETs on the internal circuit board or purchase a replacement board.


Those replacement boards must come from another Roomba and can usually be found by searching the internet.


I do offer a replacement pair of  MOSFETs for $9 including USPS shipping,  just paypal to  and specify whether you want the SMD case or the larger TO-220 package.

NOTE - The larger TO-220 case style will not fit into the same space that the original stock (SMD) smaller Surface Mount Device occupies.  The addition of some insulated wire from the SMD location to a position that the larger TO-220 case will fit into will be needed.

Click this Buy Now for the SMD 40 volt 6.4 amp pair

Click this Buy Now for the SMD 60 volt 10 amp

Click this Buy Now for the TO220 60 volt 12 amp pair

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