SLA batteries and heat

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?

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.

At 20:22 25 January 2017, wrote:
I am still using sealed lead-acid (SLA) batteries, because they are
cheap
a=
nd 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
fu=
lly 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
th=
e season I tested the charge capacity of that spare battery along
with my
o=
ther ones and some owned by our club. I found that the battery
that was
st=
ored 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
ol=
der batteries that I have. It was never used during the summer,
and its
vo=
ltage 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
we=
eks on end lost most of their charge capacity, despite being less
than 2
ye=
ars old. The latter may be due to being left in an uncharged state
for a
w=
hile, 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
cock=
pits, whether tied out or in the trailer? Not Arizona-hot, but even
in
Ve=
rmont on sunny summer days the temperature inside a glider on
the ground
ca=
n reach well above 100 degrees F.

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

The Yuasa manual for their NP batteries (probably typical SLA
batteries) has a graph of self-discharge at various temperatures.
At 0 C/ 32 F you lose about 10% of charge in a year. At 40 C/ 104
F you lose 50% charge in 5 months. Leaving a SLA battery part or
fully discharged is always a bad idea, so leaving a battery to cook
unattended over a summer is definitely a bad idea.

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 |

All secondary batteries (rechargeable) self-discharge over time.

I've read somewhere that SLA is about 1% per day, it might be higher. Lithiums are much less something like 1/10 as much. Nicad and Nickle/Hydrid somewhere in the middle.

The primary batteries have have a chemistry that will slowly lose capacity over time, You've probably got an alkaline cell that has a shelf-life of up to 10 years.

For the SLA in the hangar or trailer, there are "float" chargers that are designed to offset the self-discharge, sometimes called a "trickle charger".

My experience it that most charge-then-trickle charger systems will do quite well for a duration of several months, but eventually the battery is useless, no matter what. Reference the battery back-up systems for emergency lighting in most industrial building.

So my process is this (when I'm using SLA) one battery on the stand-by charger, one on the regular charger, when I fly, take the standby, move the other one to stand-by and when I return put the battery on the regular charger.. This way I'm rotating the usage.

YMMV

I use this in my hanger just encase.

First Alert 2013F Fire and Water Chest, 0.17 Cubic Foot, Gray https://www.amazon.com/dp/B000MPMEZ2..._B1sIyb1T5GJ8J

Heat dried the battery out, pretty simple. Batteries should be stored in cool temps, that does more for life than state of charge although that also has a bearing.

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.

[examples of not so good service...]

See the problem?

best,
Evan

On Wednesday, January 25, 2017 at 3:22:11 PM UTC-8, Charlie M. (UH & 002 owner/pilot) wrote:
Heat dried the battery out, pretty simple. Batteries should be stored in cool temps, that does more for life than state of charge although that also has a bearing.

Yes this is very likely exactly what happened. really hight temperatures cause the electrolyte to evaporate out the vents. Nobody really thought "sealed lead acid" was really sealed did they? The more correct name is VRLA or Valve Regulated Lead Acid... the neoprene valve that opens when the battery gets hot and the electrolyte evaporates out of. Which is why you want to not charge at high temp, and always charge with he battery upright so it does not blow extra electrolyte out the vent. There is such a small amount of electrolyte wetting the mat between plates you don't have a lot to start with. If you are keeping batteries at high temperatures is more likely what causes problems than sulfating issues.

And a VRLA battery discharges nowhere near ~1% per day, it more like a few percent per month in good storage conditions. Yes it increases at high temps. The ~1% per day is for old style flooded lead acid batteries. (incidentally a way I've seen folks destroy VRLA batteries is leave them on incorrect chargers over winter thinking they need to do that to avoid self-discharge issues. Nope. The incorrect chargers can just evaporate away all the electrolyte. If you are not sure you have a specific VRLA charger correctly sized to the battery that will enter float charge mode properly then just charge the battery, disconnect the charger and then recharge again at the start of the season.

Evan: I get good service (several years) out of the batteries that I take home between flights and charge right away (and then disconnect from the charger). The battery that died was the one I left in the trailer all summer. It was fairly old even before I used it for that purpose. I would have just assumed it died of old age. But, the club batteries died too. And they were only 1 year old, that's annoying. And I don't really know how often they were left in the gliders. (Nor how good are the club chargers that they get left on for long periods.)

If we were to switch from SLA to, e.g., LiFePO4 batteries (as you have), will they survive the heat for long? How long? They cost about 5 times as much... And the promised large number of "cycles" is irrelevant if they too die after a few years due to age alone. We only subject most batteries to dozens of cycles per year.