The Ultimate Telescope Battery Guide: Getting to Know Celestron PowerTank and PowerTank Lithium

There are several ways to power your Celestron telescope. Many telescope models accept standard AA batteries in a separate battery pouch or a built-in battery compartment. These work well, but if you use your telescope often, the cost of new batteries can start to add up. Unfortunately, rechargeable AA batteries can’t reliably power a telescope; they deliver just 1.2 volts instead of 1.5 volts.

Of course, you can choose to run your telescope on AC power with an AC wall adapter. This is the most convenient and cost-effective choice for permanently installed telescopes or if your observing site has access to AC power. Just be careful not to tangle or trip on the power cord in the dark.

But if you prefer to venture out to darker skies and more remote observing sites, an external telescope battery is a must-have accessory. Celestron offers five portable batteries with various chemistries, capacities, and price points: PowerTank, PowerTank 17, PowerTank Lithium LT, PowerTank Lithium, and the PowerTank Lithium Pro.

Let’s examine the differences between these batteries to determine which one best suits your needs.

Sealed Lead Acid Batteries (SLA)

 Most people are familiar with the sealed lead acid (SLA) battery. It’s a key component of your car’s electrical system and helps start your car’s engine. It works well for this application because you constantly recharge the battery as you drive. Lead acid batteries do not perform well when left idle for long periods. That’s why you need to recharge your car battery after not driving for several months. If you choose a sealed lead acid battery for astronomy, you must discharge and charge it monthly to maintain battery health. SLA batteries are a bit of a relic, but they’re still popular for astronomy and work reliably when well maintained.

Like car batteries, sealed lead acid astronomy batteries have a limited lifetime. Celestron’s sealed lead acid batteries have a lifespan of about 200-300 charge cycles.  Proper maintenance will ensure maximum battery life, but you must still replace the battery after several years.

Sealed lead acid batteries are not the perfect telescope power solution, but astronomers have trusted them for decades, and they’re a cost-effective option for people willing to put in the effort to maintain them. The original PowerTank is a smaller capacity battery, best suited for telescopes like the NexStar SLT and below. The larger PowerTank 17 works well for larger telescopes and longer observing sessions.

Lithium Batteries

Lithium batteries come in various chemistries, and not all chemistries are created equal, with some styles being better suited for astronomical use.  Here’s an overview of the most common lithium batteries:

PowerTank LT: Lithium-Nickel Manganese Cobalt Dioxide (NMC)

PowerTank Lithium and PowerTank Lithium Pro: Lithium-Iron Phosphate (LFP)

The Connection Between Battery Chemistry and Telescope Performance

Celestron tested the PowerTank Lithium LT (NMC), the PowerTank Lithium (LFP), and two competitors’ LOC batteries. The graph below shows the voltage as a function of time when using a steady load of 750mA. Notice how the Celestron batteries keep the voltage at 12 Volts over the full use of the batteries. The voltage of the LOC batteries drops below the 11-volt line after only a couple of hours of use.

Since the earliest days of computerized telescopes, amateur astronomers have improvised power solutions. In the 1980s, people used lead-acid car batteries to power their telescopes. Similarly, many competitors’ power solutions today were not designed with astronomy in mind. The small 155-watt-hour lithium batteries you’ll find online are actually repurposed power supplies for CPAP breathing machines.

CPAP machines differ significantly from telescopes in the way they draw power. Telescopes are more demanding and must consistently draw at or near 12V. Connecting LOC batteries to a telescope never delivers a full 12V and quickly loses power, tapering to 11V in less than two hours.

There are also design and application differences. To power a telescope with a CPAP-style battery, you will need a small 6-inch cord that adapts a cigarette lighter socket to accept a cigarette lighter adapter.  The cigarette lighter cord that many include is only 3 feet long, so it will not reach the power port on most German equatorial mounts when placed on the ground.

Celestron designed PowerTank Lithium LT, PowerTank Lithium, and PowerTank Lithium Pro specifically for astronomy. The high-quality battery keeps a consistent voltage until the last 30 minutes of its charge life. The design is perfect for telescopes and includes straps to attach the battery to tripod legs, keeping cords short and out of the way, eliminating trip hazards and cord wrap issues.

Some aftermarket lithium batteries have an AC adapter to power other electronics, like a laptop. Why doesn’t the PowerTank Lithium Pro come with one?

After testing aftermarket batteries, we determined that it does not make sense for a battery of this size to have an AC circuit. DC-to-AC converters are notoriously inefficient. Furthermore, these 155 Wh batteries require an internal fan to keep the batteries cool when drawing power from the AC port. Powering the fan draws electricity that should be going to your telescope. These factors render the battery less useful than its technical specifications suggest.

To demonstrate this, we hooked up a competitor’s 155 Wh battery to a single 60-watt incandescent lightbulb via the AC port. It drained in 2 hours. Of course, a lightbulb is the last thing you’d want to power when dark-sky observing or imaging. So, we tested it with a laptop. The battery’s manual claimed the maximum output was 100 watts. Most laptop chargers need between 70 and 125 watts. But running autoguiding software and image capturing software at the same time requires more power from the laptop. Unsurprisingly, the draw exceeded 100 watts, and the battery shut down after 2 minutes.

Rather than add an essentially useless AC outlet to PowerTank Lithium Pro, we included an integrated “cigarette lighter” port compatible with many telescopes and astronomy accessories.

How much power or wattage does my telescope need?

Celestron PowerTank will deliver as much current (amperage or amps) as the load (the device plugged into them) will draw. The power in watts the PowerTank delivers equals the voltage times the amperage needed to run the device.

PowerTank Telescope Compatibility List

Small Celestron mounts like the LCM, NexStar SLT, and SkyProdigy series draw about 0.3 amps when tracking, while larger mounts like the Advanced VX, CGEM II, CGX, and CGX-L draw up to 2.5 amps during fast slews. The popular Nexstar 6SE and 8SE draw 0.5 amps while tracking and 1.5 amps while slewing.

The wattage a small mount needs while tracking is 12 x 0.3, or 4 watts. The wattage a large mount needs while slewing is 12 x 2.5, or 30 watts.

The PowerTank Lithium LT (the smallest battery) delivers 73.3 watts/hour of power. A fully-charged PowerTank 17 has the highest capacity, providing 204 watts/hour of power. To determine how long a PowerTank’s full charge will last, divide this rating by the wattage drawn by the powered device. The Lithium LT is perfect for small telescopes, but if you slew a lot while observing many objects, it will only power a NexStar 6SE or 8SE for about five hours. The larger mounts combined with the 204 watts/hour PowerTank 17 will run over seven hours with similar frequent slewing. On the other hand, while tracking only, the PowerTank 17 will power a large mount for 22 hours.

The same considerations apply when using devices like dew heaters, laptops, blow dryers, and other powered astronomy accessories. The more the device draws in current, the greater the power output in watts from the PowerTank, and the shorter the PowerTank charge will last. For instance, if your dew shield heater is rated at 50 watts, a PowerTank 17 can power your heater for approximately 4 hours.

The lead-acid PowerTank and PowerTank 17 have safety fuses that limit the amperage to 15 amps, or 180 watts. The PowerTank Lithium LT and PowerTank Lithium models have a circuit breaker that will shut the battery off if the power draw exceeds three amps or 36 watts. The larger PowerTank Lithium Pro has a circuit breaker on the small telescope power connection that will trip if the power draw exceeds five amps or 60 watts, and the cigarette lighter-style socket is protected with a 10-amp circuit breaker that limits power delivery to 120 watts. The circuit breakers on all PowerTank Lithium models automatically reset after you recharge the batteries for several minutes.

 

Comparing Celestron PowerTank Batteries Side-by-side