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Interesting question. I'm not a hexpert, but I have a lot of cars
and farm/garden equipment that need batteries--including a new
EV--so I spend a lot of time thinking about batteries. I have AGMs
in both my Austin-Healeys; in one because it originally had two 6V
batteries in parallel and replacements in an appropriate size are
all but NLA, and in one because they're just flat-ass better (and I
got tired of neutralizing/cleaning acid spills in the boot--'trunk'
for you Yankees (:)).<br>
<br>
IMO, AGM are better because they seem to generally be better
constructed, and because the electrolyte--concentrated sulfuric
acid--is constrained by the fibrous 'mat.' Otherwise, the chemistry
is the same as any other lead-acid (note 'SLA,' or 'sealed lead
acid,' aka 'maintenance-free' batteries seem to be generally overall
quality and I buy them when I can). <br>
<br>
Since this question was new to me, I did some digging: <br>
<br>
<a class="moz-txt-link-freetext" href="https://discoverbattery.com/support/learning-center/battery-101/what-is-the-freezing-point-of-battery-acid-electrolyte">https://discoverbattery.com/support/learning-center/battery-101/what-is-the-freezing-point-of-battery-acid-electrolyte</a><br>
<br>
This is something I hadn't known; that the freezing point varies
with state-of-charge so, first off, if your battery is going to
endure freezing temps make sure it's fully charged. I have several
battery minders/tenders, and bought one especially for AGMs, and I
use them (the tractors sometimes sit for weeks and, when I need
them, I need them).<br>
<br>
Here's another thing I hadn't considered, but I live in the
California Central Valley and we rarely get below-freezing weather
(TL;DR: cold weather bad: "Cold weather accelerates wear and tear on
batteries"):<br>
<br>
<a class="moz-txt-link-freetext" href="https://www.relionbattery.com/blog/top-4-factors-to-consider-for-a-cold-weather-battery">https://www.relionbattery.com/blog/top-4-factors-to-consider-for-a-cold-weather-battery</a><br>
<br>
So, yeah, freezing conditions are not good for lead-acid batteries,
including AGM. I've heard the "don't store batteries on concrete"
theory, but I can't offer any explanation except that the concrete
is likely to transfer more cold to the battery (I think this is
largely an "old wives tale"). If you think your AGM is going to
experience severe cold for any length of time, store it somewhere
warmer with a smart charger (definitely not a 'trickle' charger).<br>
<br>
Bob<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 11/13/2025 11:55 PM, Philip Ethier
wrote:<br>
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<div dir="ltr" class="gmail_attr">On Fri, Nov 14, 2025 at
1:34 AM Philip Ethier <<a
href="mailto:pethier7@gmail.com" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">pethier7@gmail.com</a>>
wrote:<br>
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<div style="font-family:monospace">Absorbed Gas Mat
batteries:</div>
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<div class="gmail_default" style="font-family:monospace">OOPS. <span
style="color:inherit;font-size:inherit;font-style:inherit;font-variant-ligatures:inherit;font-variant-caps:inherit;font-weight:inherit;font-family:"Linux Libertine",Georgia,Times,"Source Serif 4",serif">Absorbent
glass mat</span></div>
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<div style="font-family:monospace">If you leave a
vehicle outside all winter in a cold climate without
charging the AGM batteries, will they be ruined by
the cold?</div>
<div style="font-family:monospace"><br>
</div>
<div style="font-family:monospace">I know that regular
lead-acid batteries can freeze up, but I don't know
about AGM batteries.</div>
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<div><span
style="color:rgb(0,0,0);font-size:12.8px;background-color:rgb(255,255,255)"><font
face="monospace">Phil Ethier, West Side,
Saint Paul Minnesota, USA</font></span></div>
<div><span
style="font-family:monospace;color:rgb(0,0,0)">2006 Gulf Stream Conquest
Super C, 8.1, white</span></div>
<div><span
style="color:rgb(0,0,0);background-color:rgb(255,255,255)"><font
face="monospace">2011 Cayman 2.9 PDK,
white</font></span></div>
<div><span
style="color:rgb(0,0,0);background-color:rgb(255,255,255)"><font
face="monospace">2021 Ford F-150 3500cc
twin turbo, white</font></span></div>
<div><span
style="background-color:rgb(255,255,255)"><font
face="monospace">1991 Caterham 1700
Super Sprint, not white</font><br
style="color:rgb(0,0,0);font-family:verdana,geneva,lucida,"lucida grande",arial,helvetica,sans-serif">
<a href="http://www.mnautox.com/"
style="color:rgb(0,24,57);font-family:verdana,geneva,lucida,"lucida grande",arial,helvetica,sans-serif"
target="_blank" moz-do-not-send="true">www.mnautox.com<br>
</a></span><br>
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<div><span
style="color:rgb(0,0,0);font-size:12.8px;background-color:rgb(255,255,255)"><font
face="monospace">Phil Ethier, West Side, Saint
Paul Minnesota, USA</font></span></div>
<div><span
style="font-family:monospace;color:rgb(0,0,0)">2006
Gulf Stream Conquest Super C, 8.1, white</span></div>
<div><span
style="color:rgb(0,0,0);background-color:rgb(255,255,255)"><font
face="monospace">2011 Cayman 2.9 PDK, white</font></span></div>
<div><span
style="color:rgb(0,0,0);background-color:rgb(255,255,255)"><font
face="monospace">2021 Ford F-150 3500cc twin
turbo, white</font></span></div>
<div><span style="background-color:rgb(255,255,255)"><font
face="monospace">1991 Caterham 1700 Super
Sprint, not white</font><br
style="color:rgb(0,0,0);font-family:verdana,geneva,lucida,"lucida grande",arial,helvetica,sans-serif">
<a href="http://www.mnautox.com/"
style="color:rgb(0,24,57);font-family:verdana,geneva,lucida,"lucida grande",arial,helvetica,sans-serif"
target="_blank" moz-do-not-send="true">www.mnautox.com<br>
</a></span><br>
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