Dee Fitz's DIY Conversation Corner

Lead Acid Batteries 101

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by , 10-03-2017 at 02:55 AM (1433 Views)
This is from a recent thread I replied to a while back.

I've long been an electric bicycle aficionado and I have a good friend who is the local Solar Power Guru where I grew up, and, well, the electrical efficiency engineer at a local municipal power company in Muscatine, IA. He and I had so many talks about batteries, I became quite knowledgeable myself regarding the "battery conversation" as he and I called it.

Once I got into using a telescope, and while doing the research on it, I found the GOTO telescopes big bane was not enough battery. So I purchased the 17amphour Celestron Powertank. Subsequent research after that on replacement batteries for it led me to believe that Celestron is not using deep cycle batteries at all. They admit this themselves when they say they'll only last about 100 cycles. Real deep cycle batteries last 150 to 300 depending on how well you baby them.

I have a hard time watching people use the wrong battery.

This is a post about how to choose, and baby your battery. Links to the best replacement you can buy included!

From an earlier conversation on this forum:

I use a 17amp battery in a car jumper pack lot cheaper that the celestron power tank well in RSA anyway , here it's not worth replacing the battery as they are similar in price , in one of my power packs the battery died so replaced with a 7amp one , it did not last long as there are a lot of rubbish 7amp batteries around that just don't last

I used to use electric bicycles, and have a friend who was the electrical efficiency engineer for Muscatine power and Water. It was a municipally owned power station.

He was a solar power guru for the local area as well.

As such, we had many conversations about batteries.

I became "knowledgeable" after many years of this.

Here's the bottom line regarding batteries. And yes, there are tons of crap batteries out there. So I've gone through some real pain myself regarding this buying the wrong type for my application.

From Wikipedia (

A deep-cycle battery is a lead-acid battery designed to be regularly deeply discharged using most of its capacity. In contrast, starter batteries (e.g. most automotive batteries) are designed to deliver short, high-current bursts for cranking the engine, thus frequently discharging only a small part of their capacity. While a deep-cycle battery can be used as a starting battery, the lower "cranking current" implies that an oversized battery may be required.

A deep-cycle battery is designed to discharge between 45% and 75% of its capacity, depending on the manufacturer and the construction of the battery. Although these batteries can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 45% discharge.[1] There is an indirect correlation between the depth of discharge (DOD) of the battery, and the number of charge and discharge cycles it can perform.
This KEYKO, 12V 18amphour deep cycle battery for $42.95 (with free shipping):

or this KEYKO, 12V 8amphour deep cycle battery at $26.60 (again with free shipping):

will out perform the original Celestron Powertank batteries by 100 or more cycles.

And they are designed to be drained to lower levels and last longer than car batteries and battery boost packs.

Although even the deep cycle batteries have some particulars to gaining the largest number of cycles out of your battery.

They prefer to be drained to 25% to 45% and no lower depending upon how robustly designed the lead plates are. See manufacturers recommendations. Regular car batteries will only drain to 70% before they can't start the car. If car batteries get drained below 70% a lot, they die very quickly.

Deep cycle batteries like the ones I've linked to have a much longer life expectancy than any other battery. Just because their plates are thicker. But still, going to the point the battery is no longer able to run your mount is going to lead to an earlier than usual death for even a deep cycle battery.

By the way, I'm convinced after the research I've done so far that the Celestron Powertank is NOT using a deep cycle battery. All reports indicate, including Celestron's own admission that they last only 100 cycles, points to the fact they are not.

So the batteries I've linked to will seriously out perform the Celestron Powertank original battery. They are designed to last 3 to 5 years in a wheelchair or electric bicycle and drain down to at least 45%.

That's 150 to 300 cycles. 150 if you find yourself draining to the point the mount no longer works every cycle, 300 cycles if you recharge before the 45% mark every time. Which is easy: Just recharge after every session and you will get the maximum number of cycles from your battery. Lead acid batteries have no "battery memory" very few batteries do in fact. The kind of batteries that have a memory effect are Nickel Metal Hydride, and nickel cadmium. See:

Batteries do not like being left sitting there drained below their efficiency point. Which is 25% to 45% for deep cycle and 70% for battery boost packs or car batteries.

So, play it safe, recharge after every session, and get the very most out of your battery.

What battery should you get? One twice the size you think you need. You want a full night out of your scope? Make the battery large enough to provide two, and recharge it every session.

This way you won't ever drain below 45%. Until you start hitting the end of your cycles.

Then you will eventually find you've lost alignment, and since you've babied the battery, you will know how long it's been in there, and not feel to ripped off, and you'll know exactly where to get the best replacement for the lowest price.

Wheel Chairs, Electric Cars, Electric Bicycles, Solar Power storage, Electric Fences, Medical equipment, and telescope mounts all have a thing in common. Failing is not an option because they're are no alternatives like "plugging in the ac adapter". They are "in the field", or essential life support units. All have Deep Cycle Requirements.

Follow up:

A member did in fact purchase the Keyko 12V 8amphour battery and found that he had to dremel the terminals on the battery down a little in order to actually fit it inside the 7amphour Celestron Powertank case. But as a DIYer, that isn't going to stop me from buying the 18maphour replacement for my 17amphour Powertank.

So the batteries linked to do in fact fit inside the powertanks. Plus they're 1 amphour larger capacity to boot. for $26.60 with free shipping.

Cannot beat that.
kingclinton and creekindian like this.


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