YAY another battery question???

[emilime75]

I have 2 batteries that are not very old but have not been taken very good care of. They have been drained down a few times by sitting unused. I have charged them both back up using a slow, low current charger a week ago and have been checking on them daily. They metered at 12.87v when fully charged, after a week of sitting they have dropped to 12.54v and 12.57v with no load. Are these OK? Is there any other way I can test them to be sure they are good enough to use in my boat? The batteries in question are standard, flooded batteries about 3 years old. Thanks.

 

[Silvertip]

Re: YAY another battery question???

They are probably ok but you can take them to any of the major auto parts stores (NAPA, AutoZone, O'Reily's etc) and have them load tested. Make sure you charge them before going however. A load test verifies that they are able to deliver the amperage stated on the battery label. Although the voltage you mention is about right, that will drop quickly when a load is placed on a bad battery.

 

[jhebert]

Re: Battery Terminal Voltage After Charging

Re: Battery Terminal Voltage After Charging

It is normal for a battery terminal voltage to rise during charging to a level that is higher than it will be once the charging current is removed. Allow a period of an hour or two after the charging current has been removed for the battery terminal voltage to reach its normal level. Use this voltage as the measurement of the battery voltage for comparison later.

A flooded cell lead acid battery will have a self discharge rate of about 1- to 5-percent of the charge per month. That is the charge, not the voltage. A loss of 5-percent of the charge corresponds to a decrease in the battery terminal voltage of 12.9-volts (FULL CHARGE) to 12.85-volts.

For more on how battery charge can be deduced from measurement of the battery terminal voltage, see

http://continuouswave.com/whaler/reference/chargeBattery.html

Your battery appears to have lost about 30-percent of its charge in one month of self-discharge. This is much more than is normal. Be sure there are no parasitic losses from dirt across the terminals.