Celestron Power Tank Battery Replacement and Mod

I recently got into astrophotography and among other accessories for my Celestron C8-SGT (XLT) telescope I purchased Celestron Power Tank. The idea is neat – Celestron combined a 7Ah 12V SLA battery in the same package with dim red light that wouldn’t destroy your night vision, 800,000 candle halogen spotlight and step down DC-DC converters that provide up to 1A of 3V, 6V and 9V to be used by other accessories like auto-guider.

The bad news were that after the initial charge my Celestron PowerTank was still dead. I’m not sure whether the battery was bad initially or it was damaged because I charged it for 24 hours rather than 16 as prescribed in the user manual. Either way I had to replace the battery.

While it is not as easy as swapping out AA Duracells in your flashlight, it is doable. You will need a Phillips screwdriver which is long and thin so that you can reach screws in their deep sockets. The only screwdriver that I had of the kind was from a precision set so it lacked a proper handle. Screws on the other hand were quite stiff. I had to use pliers to turn the screwdriver while pressing it in.

Here’s how Celestron Power Tank looks disassembled.

Celestron Power Tank Disassembled (Battery Replacement)
Celestron Power Tank Disassembled (Battery Replacement)

Everything looks good here except for 2 things:

  • DC-DC conveters aren’t of the switched-mode efficient type so your other accessories will drain battery more than they should.
  • Wires that run from battery to the terminals are way too think for PowerTank to be used as jump starter.
Celestron Powertank Battery Switch Mod
Celestron Powertank Battery Switch Mod

While 7Ah should be enough for all-night sessions unless you run anti-dew straps, it never hurts to have more power and the ability to use it without having to power down your equipment to switch to another battery. Since I already had my Power Tank disassembled I decided to install a simple mod that would allow me to do just that.

Normally the battery is directly connected to the terminals on the side of the PowerTank. From there the power is distributed to the rest of the unit, including 12V automotive sockets. I put a small rocker switch inside the side compartment where additional charging cable is normally stored. This switch can disconnect the battery from the side terminal and the rest of the Power Tank.

When the battery will start to run low, I can connect another battery/car/power supply to the side terminals to supply power to the equatorial mount and then use the switch to disconnect the Power Tank battery from the circuit. This way external battery will not waste power to charge the drained battery in the PT and there is no interruption of power supply to the mount and other accessories. If the external battery were to be drained as well, I can temporarily connect the PowerTank battery again, while I swap it out.

PS: An important note about charger that comes with the Power Tank – it is junk! It is just a power supply that will keep pumping 15V into your battery even if it is already charged. You can overcharge and destroy your battery this way. Do yourself a favor and buy a smart Sealed Lead Battery charger if you don’t have one already. A good charger will detect battery charge state and will not overcharge it even if you leave it connected for months. A good charger can also combat battery sulfation to some degree – extending the life of your battery. Since the battery is directly connected to the side terminals on the unit, you can set the Charge-Off-On switch to Off position and connect your charger to these terminals.

Clear skies and happy stargazing!

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6 Comments

  1. Hi. good mode, congrats !!! My question is more related to where did you find a replacement battery?

    TXS

  2. These batteries are commonplace – they are generally used in UPS. There is a link in a post to one sold on Amazon

  3. I removed all the screws, but still cannot remove the cover to get to the battery in my Celestron Power Tank 17. Tell me how to open it.

  4. Thanks for this great article and in particular the charger. Now I realize that I must have killed my battery by leaving it charging for nearly a week …

  5. Don
    Don’t forget to unscrew the red light cover and to remove the Spotlight (you’ll have to gently pry it off the ridged spacer after removing the nut & screw holding it.

  6. I purchased 2 power tanks for my set up.One battery died after 4 hours of use. None of the LEDs worked. I contacted the dealer, they said call Celestron.. They gave me a return number. It took 3 dozen long distance calls and 6 months before I got a replacement. The new battery died after 2 months. I got about 6-7 hours out of it. The first battery works very well, no problems at all. Im using it to power my CGE Pro mount.Canadian Tire has some real good sales on portable power packs and good warranties. Its worth looking into. Clear skies…

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