New battery. Charged for 24 hours. Light is green, but after 20 seconds light turns red and it stops.

If it is supposed to go green then the battery is not being fully charged. Unit is under warranty and now is the time to have matter addressed.

You can see the manual for the DC16 here: (
https://www.dyson.co.uk/medialibrary/Files/Dyson/Support/downloads/UK/floorcare/Manuals/dc16_uk_manual_cb_120710%20pdf.pdf )

Following the troubleshooting manual on page 6, fully charging the battery takes about 3 hours, for a run time of 6 minutes, so I'm not sure where 10 minutes comes from. The battery ships partially charged and was supposed to have been charged 3+ hours before a first use to get a full cleaning span.

It's also noted that you can get red lights if the temperature is out of an optimal range, and if the filter is not seated properly, so these would be things to check as well.
On the general checking list - look at the contacts for the battery and for the charger, make sure nothing is bent or corroded. Corrosion can be generally treated with use of some fine sandpaper or steel wool - be sure to blow the area clear of any steel wool fibers if you go that route. A better electrical contact sometimes will allow charging to get above a threshold voltage that will let the 'I'm charged' light turn green.

Good Luck! :-)

Hi.

If the red light is solid, that means that the Roomba is near to full discharge. If the light is flashing red, then the Roomba is completely out of charge.

If the Roomba is fully charged, then there may be a fault.

Here full list of light codes:

Pulsing Amber - Charging
Green - Fully Charged
Amber - Partially Discharged
Red - Almost Fully Discharged
Flashing Red - Fully Discharged"

Here manual

See also
Roomba DISCOVERY MODELS' DIAGNOSTIC TESTS

the charger is not charging its not putting any thing out into the batterys the charger clock is working but your not getting any charge from it

Sounds like you bought a defective battery
You can test for this by removing the battery and holding the power button for 15 seconds. This will restart the charging cycle as if the battery were new. If it still goes red get a refund and a new one.

Do you leave the battery on charge long enough? Try 4-hours up to overnight. If so, then the battery is probably at the end of it's useful life. Getting a new battery depends on cost versus life expectancy of the robot and whether it does the job you want it to do.

If you have a 400 series Roomba, try removing the battery, then holding down the power button for ten seconds, then recharging the unit before you run it again.

If you have a 500 series Roomba, don't take out the battery-- just press and hold the "spot" and "dock" buttons for about fifteen seconds. The Roomba will play a tune, and you can then charge it and try running it again later.

Let it charge for a full 24, or even 48 hours, regardless of the green light. If it still dies you probably need a new battery.. or worse.

I was having the same problem. Roomba would run for 30 seconds and then stop. I tried everything -- then I took the small rubber brush out and removed the small nut at the end. It was packed with dust to the point that it could not turn easily. I cleaned it out and now it is working like a champ. I think the automatic shut down was just a sign that there was too much strain to turn the brushes.

Same thing happened to me, I called the company, and they told me to remove the battery, press the on button for 5 seconds, which clears the system, replace the battery and do a long charge 12 hours. I'm in the process of doing that now.