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Battery disconnect with dual battery and trickle charger

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PostPosted: Sat Feb 09, 2019 10:45 am    Post subject: Battery disconnect with dual battery and trickle charger Reply with quote

On 1/26/2019 12:33 PM, Charlie England wrote:

On 1/26/2019 10:23 AM, Robert L. Nuckolls, III wrote:


I bought a 'no name' SLA battery through ebay back in mid November for a Kolb project that won't fly until spring. I just checked its voltage, and it's still at 12.8V. How long do you plan for the plane to sit between flights? While some have had decent luck using 'maintainer' chargers on SLA batteries, many have seen greatly reduced lifespans when using maintainers. If the battery technology doesn't need it (extremely low self-discharge rate), why risk it? Odyssey's technical documents will show you the self-discharge rate for one of their healthy batteries.

 If you have a demonstrated incident of
 death-by-maintainer, then the maintainer
 was (1) badly designed or (2) defective.

 An 'ideal' recharge/maintenance plot
 looks like this:

 Here's a measured performance on
 a Schumacher XC75 charger on a
 100AH truck battery

 Here's a plot on a Schumacher WM1562A
 on a 20AH SLVA

 Here's a Battery Tender Jr. on a 7AH

 While some do not closely follow the
 'ideal' plots, they do achieve a top-off
 followed by a drop-and-hold to the
 maintenance level. I've been
 using various charger/maintainer
 products for decades on both vehicles
 and lab batteries with expected
 results: Some of my lab batteries are
 over ten years old and still deliver
 a substantial fraction of their
 name-plate capacity. I.e. still
 over 80%.

 I've yet to test any Harbor Freight
 maintainer that produces the necessary
 performance . . . doesn't mean that
 there are none . . . just that the
 two I tested went into the round-file
 and that was over 10 years ago.

 While it's true that well constructed
 SVLA batteries may not benefit greatly
 from the use of a maintainer, it's
 not a BAD thing to do either and
 in some cases a necessary thing to do.


  Bob . . .

No disagreement that if everything is 'right', it'll be ok. But. The fact remains that quite a few a/c-application SLA users that have practiced maintainer continuous use,  report relatively short lived batteries. on the other hand, I don't recall ever hearing a report of short battery life from someone who *doesn't* have a maintainer in continuous service, even in planes that aren't regularly flown. My a/c fits the latter category; it often goes longer than a month without flying, and I've never had an issue with short battery life.

Given that SLAs can go many months with minimal self-discharge (begs the question of need), and the risk of unintentional use of an incorrect or defective charger, why go to the trouble?  Now if it's going to sit for a year...


I was one of those people who ruined a number of O-680s with a Battery Tender branded maintainer. It was established that it was an earlier version than that being mentioned here, probably manufactured circa '85.

I also managed to ruin a 680 by undercharging it in flight.  I was  just under the recommended minimum charging voltage for Odysseys and it slowly died.  I have a dual alt/batt/bus setup so it was easy to compare it to the other battery.  One lesson learned was not to put the LRC3 in such a difficult place to reach that you can't adjust the charging voltage.
All of that was an awfully expensive way to learn what was already known.
A situation I can cite that might call for use of a maintainer or top-off  is where you shutdown without the battery being fully charged.  I have 3 EFIS screens and the landing light among other things, sharing one bus.  When I land at night followed by a long taxi, I can see the bus voltage on the one bus with the pad mounted secondary alternator, is low.  I try to cross connect the 2 buses before landing at night but sometimes forget.  When I forget, I try to top off the battery.  Don't really know if it's a problem or not.

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