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I have four , 12V AGM batteries in series for 48V.

I have two, high quality 12V battery chargers.

When I measure the voltage on each battery individually, but all still connected in series, I'm seeing 12.65V

To charge them, do I need to disconnect them from each other? Or can I simply charge them each with a 12V charger while they are all in series?

Thank You
 

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you can charge each individually without disconnecting. AGM have a different profile than wet cell lead acid (13.8 max versus 14.4) check the details for your batteries, and that the charger doesn't over-charge them. i would monitor and measure voltage manually until you get confidence in the smarts of the charger--many packs (mostly lithium) have been reported as damaged on this site by overvoltage. AGM are more sensitive than wet-cell.
 

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Do NOT charge more than one unit at a time while they are connected to each other in series
unless you are 100% sure all the chargers are 100% isolated from each other

no connection between the AC side and output.

Paralleling two chargers on one unit at a time is likely fine

but also likely not to speed things up.

Figure 6-8 hours minimum depending on C-rate, if you want to get to 100% Full.

which you should definitely do for longevity, as quickly after discharge and really as frequently as possible, at least "most cycles" if you can't every time.

And get a proper charger asap.
 

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Do NOT charge more than one unit at a time while they are connected to each other in series
unless you are 100% sure all the chargers are 100% isolated from each other

no connection between the AC side and output.
Could you give a bit of information about the potential problems with this?



I have charged individual 12V batteries that are connected in series to form other multiples of 12V with 2 chargers at the same time... Haven't run across a kaBOOM yet.




Paralleling two chargers on one unit at a time is likely fine

but also likely not to speed things up.
Agreed. The charger that has even a slightly higher voltage will take the entire load unless the system is designed to share.
 

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I have charged individual 12V batteries that are connected in series to form other multiples of 12V with 2 chargers at the same time
Then the chargers involved were fully isolated from each other, and likely from their upstream sources.

If not you'd quickly see why non-isolated sources require breaking the serial connection first is required, aka shorting out.
 
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