I have brand new battery in 2012 ford focus but when I put battery in car it says low battery and the lights flicker on and off and it wont start but battery is brand new...and when i jump start it it runs fine but as soon as i turn it off it wont start and says battery low....? starter works fine no pRoblems with anything else just says battery low

SOURCE: My 2000 Honda Odyssey EX has intermittent start problems

Probably when the dealer is testing it is fine because the problem is intermittent. There may be a dead spot in the starter so when it hits that spot it acts up but other times its not on that spot its fine. Replace your starter and you will probably get rid of the problem.

SOURCE: 2002 ford explorer wont start even after new battery...

Before you go changing out the starter check for a burnt out fusible link going to the starter it will look like a wire but acts as a fuse and they burn in two just like a fuse. The symptoms you just describe are those of a burnt fusible link.

SOURCE: dashboard lights flicker s and clicking while trying to start but wont turnover or start

Sounds very much like the battery or the battery cables/connections. If the battery has low fluid or a shorted cell or two, it won't take a full charge no matter how long you charge it.
If you are not able to take the battery in for a load test and validate that it is good, try changing it out with the battery in another vehicle that is not having a problem, and see if that vehicle suddenly develops the same issue. Batteries need to have a load applied while the voltage is checked for a valid determination of it's condition. If you have a volt meter, have someone try the starter while you are checking the battery voltage. If it falls way below 12 volts (replace it), or stays above 12 volts (good) you have a valid answer either way.