macd
Well-Known Member
If at rest it is 12.5 Volts, it is suffering damage.
Can I ask what you mean by that? By 'rested' we mean left without charge or discharge, ideally for 24 hours, in order to measure the rested voltage. This was suggested because it's the simplest way which might be available to the OP of getting a reasonably meaningful idea of a sealed battery's state of charge. Or do you mean that if it's showing a rested 12.5V when it should be fully charged, it is damaged, which migth well be the case?
Of course, if you leave a battery showing 12.5V (i.e about 20% dischaged) to 'rest' for three months, it will suffer some self-discharge and maybe some slight erosion of its capacity, but it certainly shouldn't wreck a healthy battery.
Yes, you'd be wise to consider a battery as having nothing more to give at 12.1V, and it might struggle to start an engine (but not the OP's). But it would by no means be flat.12.1 volts you are looking at a flat battery.