What can cause my Homelite cordless lawn mower UT13126 to stop after 3 minutes when the battery is fully charged

ck the battery connections for tightness also there is an inline fuse , that is located right off the positive battery connection as well

check the battery condition as it may have 24 volts but very little when the motor is trying to spin
check that the blades spin freely by hand to ensure that the motor is not seizing up

the motor is bad

try running the battery right down to fully flat this should reset the diods to fully recharge the battery again

The batteries are defective in this unit. It should be returned to the dealer that you purchased it from and get exchanged, or your money back. Another way to test this mower is to charge the batteries fully, then test them. If they are truly fully charged, run the mower until it slows down, and test the batteries again. If they are still charged, (unlikely) then the problem is in the motor itself and still should be returned.

batteries may not have enough power if there old you may need new ones

Check the switch for current flow with and without the key. Then make sure the ground switch is disengaging when you pull the handle.Possible stretched cable.

your batteries aren't charging fully, check them fully charged with a volt meter,, fully charged they should have a reading of 18.5 volts, if not they are not charging, and either the batteries have used up their life, or your charger is on its way out

The batteries need replacing - this will probably happen every 2 years, maybe 3 if you're lucky. It takes standard sealed lead-acid (SLA) batteries that your local battery store should carry. Be careful not to charge your mower when it gets like this as you will fry the charger like I did.

When batteries are only used seasonally, and they are stored, they can become damaged from weather or from storing them when they are not fully charged. In general, batteries used seasonally will have a shorter lifespan, so it sounds like you likely need a new battery. Check out http://www.batteryinternational.com/electric-lawn-maintenance-batteries.html for a replacement, and be sure to charge it fully before storing.