laurieoz wrote:

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Possum3 wrote:

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Laurie you will need to check voltage with a voltmeter - Eight year old AGM Batteries would definitely be near the end of their life.

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I have had the batterys disconnected for 4 days

Still 12.83 Volts today

Can the voltage stay up but the capacity of the batterys drop?

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 The resting voltage is a fairly accurate method of determining the state of charge of a battery. However you have to remember that as a battery ages and loses capacity the resting voltage of the battery remains about the same as that of the battery when it was new. What you must remember is that the older a battery gets, its capacity reduces. If you have a battery that started its life as a 100Ah battery, when you measure the resting voltage that has lost 20% of its capacity, when you use the voltage/SOC chart to estimate the amount of charge in the battery, you treat that battery as an 80 Ah battery.

In other words, the battery that has lost 20% of its capacity will only have 40 Ah left when the standing voltage says it is half charged. Likewise, that battery, when it has lost 40% of its capacity will only have 30 Ah when the chart indicates that its SOC is down to half charge (i.e. it is now only a 60 Ah battery.) That is similar to the estimation that the battery monitors do when they compensate for the ageing of the battery they are monitoring.

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