Gel Cycle Life [RE-wrenches]

Doug Pratt dpratt at pacific.net
Wed Apr 9 19:22:17 PDT 2003


Hi Travis,

  Real Goods has been selling the MK gels under private label for 5-6
years. I also seriously questioned those same somewhat amazing cycle
curves before we took them on. The tests were NOT done by MK, or even by
the German licensee, Sonenshein (sp?). These were true independent
third-party tests of random batteries pulled off the assembly line. Get
MK to cough up the original test results, they're impressive, and so far
I can tell, totally impartial. (Memory is vague, and I'm writing from
home without all my hard-copy files, but I think it was NREL decided
these were the best batteries they'd ever tested.)
  In the years we've been selling these batteries I've been nothing but
impressed, with both the batteries and with MK's great service. They've
bent over backwards warranting batteries that MIGHT have been defective,
but MIGHT just as well have horribly abused. (Over the phone, everyone
has treated their batteries like a religious object.) We started out
telling folks to expect a 2-4 year life. With no (known) failures yet,
I've upped that estimate to 5-10 years. 
  Hey, you think the smaller batteries have impressive curves? Check out
the cycle curve on their golf-cart type battery. It went 1000 80% cycles
and wasn't even fading yet when the tester gave up and shut the test
off. (Pricey bastard however...)

Cheers,
Doug Pratt
Real Goods Technical Editor

-----Original Message-----
From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net] 
Sent: Wednesday, April 09, 2003 12:34 PM
To: RE-wrenches
Subject: Gel Cycle Life [RE-wrenches]

Hello All,

I am looking at using some MK gel batteries on job where maintenance is
likely to be a problem (and how is that different than any other job?).
The
customers seem interested in paying more for no battery maintenance.
The MK
batteries are priced very well if you know where to buy them.

It's a weekend hunting camp that's likely to be heavily discharged, 80%
or
more DOD, when it's used approximately once per month.  Still, that's
many
years according to the factory cycle curve.  And yes, I'm worried about
charge regulation which makes the NVRAM of the Outback equipment
especially
attractive.

The MK Gel battery cycle curve shows 
2500 cycles @ 25% DOD
1100 cycles @ 50% DOD
750 cycles @ 75% DOD
500 cycles @ 100% DOD

The MK AGM battery cycle curve shows 
1200 cycles @ 25% DOD
500 cycles @ 50% DOD
250 cycles @ 75% DOD
200 cycles @ 100% DOD

I always thought AGM's were much better cycling batteries than GEL?  The
GEL
cycle curve is almost unbelievable.

Anyone else think that GEL cycle curve is way out of line?

Travis Creswell
Ozark Energy Services

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