Mike Palko did a nice article on this in control line world a couple or four years ago -I dont have the mags anymore - but from memory the CCA has nothing to do with capacity - it is the deliverable power at startup. capacity is waht you are looking for and a deep cycle - so it will provide the required amps for a long period of time.

Hi Linheart,

I got your email, but I thought it would be best to reply here for everyone’s benefit. This is taken directly from my article in the July 2009 issue of CLW.
To calculate the deep cycle capacity required take the lipo capacity used per flight and multiply it by the pack voltage to attain watt/hours (Wh).

16.8v x 2.5Ah = 42Wh

Multiply the watt hours by the number of charge cycles you require per flying session.

42Wh x 5charges cycles = 210Wh

The depth of discharge not to exceed for lead acid batteries is 50%. Since 210Wh is 100% we need twice this.

210Wh x 2 = 420Wh

The total deep cycle battery capacity required would then be 420Wh / 12v = 35Ah.

Cold cranking amps and reserve capacity are not directly related capacity. You can estimate the batteries capacity using them, but it is always best to start with a known capacity. I mention all three methods in CLW and can describe them here if people are truly interested.

As for real world experience I use a 75Ah battery and get about 6 to 7 charge cycles per session (5S and ~2,800mah used). With each passing season the lead acid battery degrades just like our lipo’s. I get about four seasons per deep cycle before I have to buy new. That’s if I maintain them which doesn’t always happen.

Mike 

John,

Car batteries (starter batteries) should not be used for deep discharging applications. Anything more than one or two charges from a starter battery per flying session will shorten their life span. The internal design of a deep cycle battery is different than a starter battery. They are much more robust and are purpose built. The 50% rule is only for deep cycles.

A trickle charger should be used for both starter and deep cycle batteries when not in use for extended periods of time. Lipos should be stored partially charged, while lead acid should be stored fully charged.

Mike

Allan,

A quick google search turned up this link which gives and explanation of the three (starter, marine, deep cycle).

http://www.windsun.com/Batteries/Battery_FAQ.htm

Looks like a marine is a hybrid which I did not know myself. There is almost too much info in the link!

Mike