Mix Old (2yr) AGMs with new?

[roaming]

I am looking to add 4 more AGMs to my existing 4 Deka 8AGC2 190ah AGMs that are about 2 years old since we're installing solar. Can you mix older AGMs with new, or is the a no-no like with wet cell?

Thanks!

[GaryKD]

Hi roaming,
This brings up the debate between engineering and reality. If you know the history of the current set of batteries and they are still in great shape, go for it. If it was me, I'd just add the 4 new batteries. The purists will post "the sky will fall" if you do this. For me, I'd give it a try.

[roaming]

Thanks for the reponse Gary.

I assumed as much, since the batteries are fairly new, but I thought I'd see what the folks here said. I hate to put an extra grand into replacing 4 perfectly good batteries just to ensure that they're all the same vintage, especially since i heard that 2009 was a great year!

[wardy]

As long as they are in parallel I would add new to the old without hesitation if the older batts are in fine order. At some point though depending on use etc the older batteries will fail before the new. With that in mind it would be prudent to check every after say three years of age (older batts) for condition. This way you'd find out in a reasonable period if the older batteries were causing the converter to over-charge the newer cells shortening their usable life.

[roaming]

Great info as well, thanks wardy! I just had these load-tested and they were 95%+, so I'm pretty comfortable adding the additional batteries in parallel.

[wa8yxm]

First the thing about "All batteries must be the same age" only applies to batteries in SERIES like six volt pairs. It does not apply as much to batteries in parallel (and that includes two pair of six volts pair to pair, it only applies within each pair) however I do admit there is a SLIGHT chance of damage.. two ways, and one of them is very very rare with AGMs.

The greatest danger is shorted cell, Batteries fail one of two ways, Shorted cell is very rare indeed in AGM's but if it happens then you have a 10 volt battery and a 12 volt side by side, this will cause the good one to deep discharge, and the bad one to charge too fast which can cause a battery "Exploison" Again very rare with AGM's

(And not that likely with flooded wet either)

The other chance is high resistance.. IF your converter is large enough, this can damage the "Good battery" by too rapidly recharging... However epically with AGM's this is not very likely either.

So I'd say "GO FOR IT"