I know when shopping for wet cell batteries it is always best to buy ones that were made within the last few months. While probably still a good idea to get as fresh as possible, does the same importance of freshness apply to AGMs? i.e. Do not buy if more than 6 months old...
I thought I read that shelf life was much longer for AGMs....
AGM's self discharge a LOT slower than flooded batts so they can sit without a charge (with no load of course) for quite a while, especially if they're kept relatively cool. Charging them every 3 months or so is not out of line.
Are you asking about shelf life before or after activation? A number of brands/sizes of AGM are shipped dry, with electrolyte packaged separately. Those will store indefinitely until activated. They can be manufactured years before, but are "new" until the electrolyte goes in.
Once activated, shelf life starts. My experience, up to a year they seem to be OK. Two years storage without maintenance charging, they can lose service life or fail. The failure mode I am most familiar with is a cell shorting, often under heavy load only, which makes the fault hard to diagnose without load testing.
Even on a maintenance charger, 3-4 years is stretching expectations of the battery remaining useful.
My AGM experience is mostly small 12V AGM starting batteries, Japanese manufacture and Chinese clones; the clones do worse. Your experience might be different with larger AGMs of different design and application. Spiral-wound cells are a whole different territory.
PS. Was a time, 50's through 70's, flooded wet cells were shipped dry, filled (activated) when first put in use. I remember activating them, pouring acid from a PurePack wax container. I remember brands advertising this "freshness" as a feature. This may have been an older practice, we used to keep carboys of electrolyte around the shop when we did this type of general service. I suspect occupational safety standards led to wet cells being shipped wet.
* This post was
edited 05/20/12 05:35pm by tatest *
tatest wrote: Are you asking about shelf life before or after activation? A number of brands/sizes of AGM are shipped dry, with electrolyte packaged separately. Those will store indefinitely until activated. They can be manufactured years before, but are "new" until the electrolyte goes in.
I have always been under the impression that AGM ie Absorbed Glass Mat batteries were sealed when they were manufactured. I did not think that there was any way to add electrolyte later and were basically hands off "maintenance free" If this is the case and the glass material is always impregnated with just enough acid at the factory to last the lifetime of the battery then I am thinking they come activated. That being the case I am thinking that the fresher the better as with most battery types. My AGM's are this type.
Jonesz
* This post was
edited 05/21/12 03:31pm by Jonesz *
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