SLA batteries and heat

On Wednesday, January 25, 2017 at 3:22:22 PM UTC-5, wrote:
I am still using sealed lead-acid (SLA) batteries, because they are cheap and give good service for several years in my experience. The power needed in my glider is modest so even on a long flight the battery does not get fully discharged, that lengthens its life. I take the battery home when I am done flying, charge it, and keep it in moderate temperatures.

Last summer I kept a spare battery in the glider trailer, in case I forget to bring a battery to the airport when I go there to fly. At the end of the season I tested the charge capacity of that spare battery along with my other ones and some owned by our club. I found that the battery that was stored in the trailer was pretty much useless, even though it was good before that summer, and not that old. It held much less charge than some much older batteries that I have. It was never used during the summer, and its voltage held up, but measured capacity (amp-hours) was reduced to a fraction of 1 AH by the fall.

Also, some club batteries that were perhaps left in the club gliders for weeks on end lost most of their charge capacity, despite being less than 2 years old. The latter may be due to being left in an uncharged state for a while, I don't know, since the club does not keep battery charging records.. But it could also be due to the hot summer temperatures in the glider cockpits, whether tied out or in the trailer? Not Arizona-hot, but even in Vermont on sunny summer days the temperature inside a glider on the ground can reach well above 100 degrees F.

So, is it useless to store a spare SLA battery in the trailer?

Google "Battery Care and Maintenance Darryl Ramm Pasco 2006" - it's a .pdf file. It is an excellent summary. Short answer - yes.

On Wed, 25 Jan 2017 13:00:39 -0800, Dan Daly wrote:

On Wednesday, January 25, 2017 at 3:22:22 PM UTC-5,
wrote:
I am still using sealed lead-acid (SLA) batteries, because they are
cheap and give good service for several years in my experience. The
power needed in my glider is modest so even on a long flight the
battery does not get fully discharged, that lengthens its life. I take
the battery home when I am done flying, charge it, and keep it in
moderate temperatures.

Last summer I kept a spare battery in the glider trailer, in case I
forget to bring a battery to the airport when I go there to fly. At
the end of the season I tested the charge capacity of that spare
battery along with my other ones and some owned by our club. I found
that the battery that was stored in the trailer was pretty much
useless, even though it was good before that summer, and not that old.
It held much less charge than some much older batteries that I have.
It was never used during the summer, and its voltage held up, but
measured capacity (amp-hours) was reduced to a fraction of 1 AH by the
fall.

Also, some club batteries that were perhaps left in the club gliders
for weeks on end lost most of their charge capacity, despite being less
than 2 years old. The latter may be due to being left in an uncharged
state for a while, I don't know, since the club does not keep battery
charging records. But it could also be due to the hot summer
temperatures in the glider cockpits, whether tied out or in the
trailer? Not Arizona-hot, but even in Vermont on sunny summer days
the temperature inside a glider on the ground can reach well above 100
degrees F.

So, is it useless to store a spare SLA battery in the trailer?

Google "Battery Care and Maintenance Darryl Ramm Pasco 2006" - it's a
.pdf file. It is an excellent summary. Short answer - yes.

My club's batteries are kept in a cupboard in the club house/office
building when not in use. At the end of a day's flying they are taken out
of the gliders and connected to a multi-stage charger (we have one for
each battery) so they are back on charge charge shortly after flying has
ended and remain there, on float mode, until their next use.

I do something similar: I have a pair of chargers (one for each flight
battery). I keep my batteries at home, putting them on change as soon as
I get home and taking them off charge when the charger shows its in
'float' mode - that may be later that evening or next morning. They are
left in a fully charged state in my indoor workshop until next time I fly.

FWIW I'm still using Yasa NP12-7 SLA batteries. Yuasa are the most
reliable brand I've found (much better than uniRoss) and their price is
reasonable. I run a charge-discharge-recharge cycle in each battery when
I first get a new battery and repeat it once a year, replacing them as
they drop below around 60% of nominal capacity. For Yuasa batteries that
is generally after 3-4 years service, though recently I've had one or two
that failed on their 12 month check - I think a lot are now made in China
rather than at their factory in Gunma Prefecture, Japan.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |