[gpeden]

Originally Posted by Shawnlh

Any true deep cycle will work. Just be sure to grab the one that has the highest amp/hour rating. I would suggest at least 120 amp/hours, which should give you back about 12,000-15,000 mAh's into your packs.

Hi,

For charging capacity calculations relative to larger packs, you need to consider volt-amp-hours, not just mAh's. For instance a charging battery is 12V and a 6S battery is about 24V. A 120 amp-hour battery contains 120,000 mAh's FWIW and that would be a good, large RV battery The RV battery I own is about 100 AH's.

I've played with the math before, starting back when I was using these batteries to charge 20 to 26 cell NiCad packs. Let's say you want to know how many 6-S 5000 mah packs you can charge with a spiral cell battery (I had two of the yellow tops), which I believe were 55AH batteries. Assuming that one can get about 75% useful capacity out of this battery (useful capacity of battery drops off sooner when sucking 20+ amps out of it charging at 2C or more), you'd have:

55AH x 0.75 x 12V = 495 VAH

To charge one of the 6S - 5 AH packs mentioned above (assuming 75% efficiency in the charge process), you'd need:

6cells x 4.2V x 5 AH x 1/.75 = 168 VAH

In reality you'd be lucky to get three charges. A you can see, one would not get too much use out of smaller batteries if using larger packs. The so-called power packs offered for sale are usually about 18-26AH only. And one would be crazy to charge larger packs off a car battery, because they are designed for short bursts at high amps, NOT to be run all the way down, and it would die an early death.

These days, the largest packs I deal with are 6S 3700's. The worst case "roughing it" scenario is where I setup camp for a week or more at a flying field with no available 120V power. I used to have to haul away the batteries every night for charging. My life has dramatically changed since I bought a nice 1000W Yamaha generator after a good weekend at the poker table I purchased 2 new AGM deep cycle batteries ( I think about 75 AH) from a battery distributor to use in series as a 24V source with my Hyperion 720iNet3 charger, which is more efficient when used with up to a 28V source. You can tell they are good, because they are freakin heavy for their size I use the old RV battery for other chargers. It is much more efficient to use the generator to charge multiple deep cycle batteries at once (less noisy time too, although it is super quiet), so I have 3 deep cycle chargers and use them to give 8 amp charge rates to the 3 deep cycle batteries simultaneously, usually at the end of the day, while also charging the trailer battery and running the trailer on 120V so we can charge laptops, flashlights, cameras, music machines and enjoy brighter lighting when needed. If I used just the genset for flight pack charging, then it would be running all day....

[Shawn_1976]

At our field I put up a 20 watt solar panel with two 6V 232AH golf cart batteries. We have tonnes of power. I sell this stuff. If anyone is interested send me a pm. I would gladly help out

[gpeden]

Now THAT would be nice! But a good fun fly would suck the life out of those all the same

[Xanadu]

Deep cycle battery's are a lot heavier than a regular battery, so just be careful how large of one you get. Give yourself a hernia lifting in/out your trunk, etc. Need a wheeler to transport to the field as well, or a wagon.
Next thing you know, we will be loading the kitchen sink as well!..........

[Shawn_1976]

We keep the deep cycles at the field year round with the solar panel maintaining it. Ya, a fun fly would use them up fast. Most of our club is nitro