It won't take long to realize that using AA batteries is an expensive way to feed your NexStar (for those models that offer this option). For a good number of weeks I used two 6 volt lantern batteries - a NexStar GT will run for days on that power. If you are interested in using this option, but don't already know how to make the required cables, I would advise against it as it can be easy to reverse a connection and damage your scope. And in any case lantern batteries are still too expensive.
So obviously what we really want is a rechargeable power source or an AC adapter. NiCad and NiMH batteries won't do (unless you make your own battery holder) as they only produce 1.2 volts as compared to the 1.5 volts of an alkaline battery. NexStar telescopes require 12 volts to run correctly, so you would need 10 correctly connected NiCad or NiMH batteries.
Any AC adapter providing 12 volts and at least 1.5 amps should work fine for the smaller NexStar scopes, though many wall transformers have suspect power and have been known to cause problems. CGE, CGE Pro, CGEM, GPS and Advanced Series scopes also require 12 volts, but they require much more current than is available using small batteries or most AC adapters. At a minimum, you will need an AC adapter providing 2 full amps for these models, 3 amps would be recommended. A power supply which provides regulated output voltage is highly recommended. One good source for a regulated AC to DC power adapter is www.ScopeStuff.com. Whatever power source you choose, the correct connector to attach to the scope has an inside diameter of 2.1mm and an outside diameter of 5.5mm with positive (+) on the inside conductor. 2.5mm inside diameter is much more common and provides a loose connection that causes MANY problems in the operation of the scope. The CGE Pro uses a new threaded power connector - a nice change as it cannot be disconnected accidentally - but it is compatible with the old style NexStar power connector if needed. More info on the power connectors for all these mounts can be found here.
While AC adapters are in some ways convenient, my recommended power source for all Celestron computerized telescopes is a rechargeable 12 volt battery with 7 amphour or greater capacity. The higher the amphour rating, the longer the battery lasts between charges. You can buy 12 volt rechargeable power sources on most astronomy equipment web sites - sometimes they are referred to as field power packs. Celestron and Orion offer small 7 amphour models that will run even the larger scopes for several hours and larger 17 amphour models that will run a scope for an all-night session with ease. These power packs also include power jacks for 3, 6 and 9 volt accessories and have red and white light flashlights built-in. Both the Celestron and Orion power packs are based on sealed lead-acid battery technology.
A few additional notes on rechargeable power sources based on sealed lead-acid battery technology. To prolong the life of the battery, recharge after every use. Do not wait until the telescope starts acting sluggish or the meter on the battery indicates low power. Also, if the battery sits unused, charge it at least once a month. You should also be aware that, overcharging can easily damage and most do not include a recharger with automatic shutoff. NexStar Group member Phil Chambers provided the following tip. Plug the charger into a power outlet timer (the little gizmo used to turn lights off and on to deter burglars while you are away) with all the 'ON' pins removed and only a single 'OFF' pin inserted. Then you can set the timer to shut-off after the recommended recharge period, generally no more than 12 to 24 hours. Another option is to purchase a trickle charger from a marine or automotive parts store. While more expensive, it will keep your battery in top condition. Be aware though, that some rechargeable power sources have electronics that prevent a trickle charger from working properly and that there are a couple of different battery technologies used, each requiring a different type of recharger. So, you may only learn by trial and error if a particular trickle charger works for your battery pack unless you are very familiar with battery technology.
Learn more about rechargeable batteries by reading Jim Towers' guide on the subject, found here.
Finally, you will need to supply the correct cord to go between most battery packs and the scope. Astronomy dealers that sell Celestron equipment can provide the cord or you can try an electronic parts store like Radio Shack in the US. The cable you are looking for has a cigarette lighter plug on the end to connect to the battery pack and the plug for the scope end has an inside diameter of 2.1mm and an outside diameter of 5.5mm with positive (+) on the inside conductor. Note that the more common connector is 2.5mm inside diameter. This will not provide a positive connection and leads to many problems with operation of the scope as momentary power interruptions cause misbehavior of the electronics of the scope. Again, the CGE Pro uses a different power connector and includes a power cable with the required cigarette lighter plug.