Maintenance Free Battery Impedance Value

<...Can any one update...>

Yes. The Maintenance Manager at the facility is the next person to speak to.

Batteries should be replaced max 10 years, depending on critical nature of the application could be much sooner....How old are the batteries?...also impedance must be in context to temperature which varies with temperature and SOC...

As Solar Eagle pointed out, it is relevant whether your measurements are at a cell temperature near to the OEMs specification. Generally, temperatures above the rated value have little effect with a new battery [but life falls a lot at high temperature]. Temperatures below rated usually have a big effect, reduced voltage/increased impedance, especially below 0'C.

All batteries have a tolerance between samples.

It is always much more significant to make tests at regular intervals on each installation, with the same test gear and recorded result & temperature. A downward trend for the same conditions can then be identified, despite any seasonal variations over a year. This is particularly valuable when there are a number of series blocks, a drop at one block will stand out when the total battery effect may not be significant.

So...

1. how long have you been making "3 month" tests?
2. Do you have results for each battery [cell/block??] of your 64?
3. Do you see any rising impedance over time?

A simple and definitive test is to put the UPS load onto battery and look for blocks with fast falling DC voltage compared to others at discharge times less than the rated reserve time. Since series blocks have the same ripple current from the inverter, an AC voltage measurement on each block will show an increase in impedance as an AC voltage increase for a block which is exhausted.

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