# Marathon 40SP100 Nicads



## madderscience (Jun 28, 2008)

OK so I was at the dump today, and (me being well.. me ) I had to go look at what other people had dropped off. In the pile of scrap batteries was this: (see attachment)

A marathon 24v, 40AH aircraft starting battery. Turns out it contains 20 Marathon 40SP100 flooded NiCd cells. I had to rescue it.

This type of nicads (usually the somewhat smaller 34AH BB600 though) are probably the second most common type of battery seen in homebuilt conversions after lead acid. 

Too bad there weren't 9 more of these; that would have been a roughly equivalent traction battery to the one I have now.

So the dumb question now, is: Does anybody know of a source for more of these (surplus) and what fair market value for good used cells is for this type of battery?


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## david85 (Nov 12, 2007)

Wish I could help you with finding more, but I have to ask, does it still work? I'd like to know because if I read the date correctly, thats 13 years old.


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## madderscience (Jun 28, 2008)

flooded nicads are known for having quite long service lives. The surplus BB600's I've seen used in EVs are often 20 years old.

The first 10 (to match up with my 12v car battery charger) are charging up now. They all cleaned up to the point where they look new. When put on the charger they started taking current and came up to voltage instantly. The plates (visible through the translucent battery cases) all look practically new.

I'll find some way to do a rudimentary load test on them to see how good they are but I suspect they are fine.


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## TX_Dj (Jul 25, 2008)

madderscience...

My only recommendations would be to either contact your local battery recyclers and tell them you are interested in buying batteries of this type and capacity, and/or contact various A/P shops to let them know you'd be interested to buy any pulled units they come across.

I would love to get my hands on a couple hundred Ah of nicad like those for use in my truck, especially if the price was comparable to lead acid or less.

I do worry though about the myths and rumors associated with NiCd "memory", I know not all NiCd suffer from this, but I know too little to tell.


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## order99 (Sep 8, 2008)

I assumed that all NiCads had a memory effect...but i'd be very, very happy for madderscience if I were wrong! Of course, the only NiCads i'm truly hands-on familiar with are from the older-model computers and Cordless phones...

If there's no memory effect then maybe NiCads would be a decent stand-in until Chevron(HISSSSS!!!!) releases my lovely NiMHs from bondage or until the Lithium variants drop in price a few more times.


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## madderscience (Jun 28, 2008)

these batteries are used for starting airplane engines, which I imagine like any starting battery is very high power for a short period of time and doesn't really discharge the battery. So if memory effect was a problem they would be useless. There are about 50 cars on the austinev.org evalbum using flooded Nicd, so methinks they are OK in that regard.

I've gotten in touch with a local EV fellow who is familiar with this battery type, he will be helping me revive them. (though my simple test, a low-amp charge for a few hours has brought them all up to voltage, and I ran an automotive 12V inverter powering a 100W light bulb off one of the strings for several minutes, so I think they are all alive...)


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## order99 (Sep 8, 2008)

madderscience-PM sent.


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## e_canuck (May 8, 2008)

Hi all.

NIcad as it pertain to aircrafts. They will give high amperage for engine starts. Plus they will discharge at a very predictable rate before dying out all together.

They do develop a memory. And that is why they need to be deep cycled regularly. The deep cycling is normaly done in a battery shop by a trainned technician. I would say never discharge them below 22V in normal use.

As the individual cells discharges some will deplete faster than other. If cells get to zero they can then start charging from the other cells. Not good. This reverse current lead me to my next point.

NIcads are also prone to thermal runaways. Aircrafts equiped with them will have thermal sensors so crew can tell the batteries temperature as well as temperature switches to alert them of a possible runaway.

There are several causes for the runaway. Overcharging, faulty cells, charged improperly, etc.

They are good batteries with good qualities for an aircraft. Good amperage for engines starts plus good reserve for backup in case of total generator failure in flight.

They are also costly to get and costly to maintain properly. A lot of operators have replaced their Nicads with lead acid batteries.

Be safe,

DP


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## aeroscott (Jan 5, 2008)

i have some old ones that look the same (same size )but are 20 amp h. and not the sintered cell type . a big gain in energy . super long life. great find


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