My sons razor e200 dies quickly. I have changed the batteries, brought a new charger. I have checked the connectors and the tires are not flat The light is green but after 25 yds, turns and says needs to be charged.

check the areas by the tires and charge battery fully. first start on a very small hill or maybe your drive way.

the battery is probably dying out and you need a new one, or need to charge

check your charger and batteries with a multimeter and make sure that they are showing the proper voltage, also visually inspect the batteries for bulging or swelling, probably one or both of the batteries are bad

First check if it's the charger or battery that was defective. Unplug your old charger, and test it with a known working charger, see if the problem gone, if yes, then you need to replace a new battery charger.
Razor E200 scooter battery charger
Razor E300 scooter battery charger

Depends, some tabs are directly soldered to the batteries themselves so you will need a soldering iron to remove the tabs. After that, it wouldn't be too hard to remove and replace.

Keep in mind that these take 2x12volt batteries and these lead-acid type batteries may take a long time to charge depending on the current your charger is supplying.

If you plan to charge the two batteries with the stock charger, then you would have to wire the 2 batteries in series for 24volts (stock charger 24v) and for convenience you may also want to head out to your local electronics store to see if they have the female socket that the charger goes into, and possible some wire, connectors/tabs that attach to the batteries and possible some small alligator clips if required.

Buy a replacement battery pack and charger at razor.com or http://electricscooterparts.com/razore300.html

Click this link http://www.razor.com/support/pdf/manuals/current/e100-series-manual.pdf

Scroll down to chain and tire replacement. It has a full exploded diagram of the rear wheel

This could be a sign of a dying battery, although it charges and lights the green light it cannot maintain enough juice to power the machine when it has weight on it.