NexStar Evolution owners, read this article.
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 for 10 batteries) 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. All of the GEM and the larger fork mounted scopes require more current than is available using small batteries or small AC adapters. At a minimum, you will need an AC adapter providing 2 full amps for these models; 3 amps is recommended. On any mount where you have added the GPS or StarSense accessories, 5 amps is recommended. A power supply which provides regulated output voltage is required. One good source for a regulated AC to DC power adapter is www.ScopeStuff.com.
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 a lead-acid battery and most of these power packs 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 packs 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 lead-acid batteries by reading Jim Towers' guide on the subject, found here.
More recently, lithium-based battery packs have become available. Celestron's PowerTank Lithium (part # 18771) is one example. Based on environmentally-friendly LiFePO4 battery chemistry, this power pack provides about 7 amp hour of power and unlike lead-acid batteries, can be used to nearly complete exhaustion. It charges from empty in 4 hours and does not require maintenance charging like lead-acid power packs. And, the battery sports a 2,000 charge lifetime compared to about 300 charges for a lead-acid battery. It even includes a USB port to provide emergency power for your smartphone or tablet.
Another great choice is a 12 volt battery pack designed for LED strips and cameras used in stage productions. For examples, search for TalentCell on www.Amazon.com. These battery packs recharge quickly, retain their charge for long periods of time (no maintenance charging) and are small and lightweight. In fact, you can easily attach one to the fork arm to eliminate cord wrap issues.
Finally, you will need the correct cord to go between most battery packs and the scope. Astronomy dealers that sell Celestron equipment can provide the cord which goes from a power source with a cigarette lighter outlet or you can try an electronic parts store like Radio Shack in the US. Other power sources may require cables specific to them. In any case, 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 some cables have a connector with 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. The CGE Pro and some of the other large Celestron mounts use a slightly different threaded power connector and include a power cable with the required cigarette lighter plug. More info on the power connectors for all Celestron mounts can be found here.
One final note, connecting the power backwards will cause severe damage to the electronics of your telescope. The inside conductor of the power connector MUST be the positive terminal.