Simon_CSK Posted August 31, 2015 Share Posted August 31, 2015 I bought an Optima battery nearly a year ago for my Discovery. Over the last few weeks it has been loosing power overnight and now will not retain enough charge to start it between starts. I have switched to an older battery I had and have charged the optima out of the car. The battery is currently sitting after a charge at 12.3V. Is this good or bad? I thought it should be 13.5 volts it sat at. Help and advise appreciated. Quote Link to comment Share on other sites More sharing options...
elbekko Posted August 31, 2015 Share Posted August 31, 2015 13.5V is with the alternator charging. 12V-ish at rest is normal. Check what it does when a load is added. Quote Link to comment Share on other sites More sharing options...
simonr Posted August 31, 2015 Share Posted August 31, 2015 12.3 is a little low - though your volt meter could easily only read +/-5% so it's not absolute. The graph above is for a battery at rest - no current flow and is fairly accurate for a battery in good condition. Elbekko is right that to determine the health of the battery you need to load it and see how fast the voltage falls. This gives a good guide to the remaining capacity of the battery. As batteries age, the capacity falls (causing the voltage to drop under load faster). Optima's are great batteries, but they are sensitive to abuse. Mainly over-charging or over discharging. They can often be brought back to life with a 'conditioning charger' such as one of the CTek range. You have to leave it conditioning for a few days to have a decent effect - but they can rescue a knackered battery surprisingly often. Your Alternator should charge at up to 14.6V. Any higher will damage the battery. Immediately you take it off charge it should show about 13.8V (or more) sinking quickly to 12.8V Si Quote Link to comment Share on other sites More sharing options...
SPendrey Posted August 31, 2015 Share Posted August 31, 2015 You might also want to chase around for other causes, i.e. something that is draining the battery for you. It may not be the battery itself that's gone bad? Quote Link to comment Share on other sites More sharing options...
cackshifter Posted September 2, 2015 Share Posted September 2, 2015 Yes agreed, 13.5 with the alt charging suggests to me the alt has gone soft - mine do 14.4 even at tickover. Maybe a diode has gone, or the sliprings are dirty. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted September 2, 2015 Share Posted September 2, 2015 *some* alternators aren't regulated to 14.4V, but 14V, my Audi included. Normally shows 13.8V at battery terminal when running or revving, so check your stickers/regulator casing. Quote Link to comment Share on other sites More sharing options...
Simon_CSK Posted September 2, 2015 Author Share Posted September 2, 2015 The Disco does have electrical gremlins however having put in my spare battery I have not had any issues and the car had been laid up some days when I use my Range Rover which confirms to me that the battery has issues. Not yet had time to check it out hopefully get some time tomorrow. Quote Link to comment Share on other sites More sharing options...
cackshifter Posted September 4, 2015 Share Posted September 4, 2015 Optima recommend charging at alternator volts 13.3v to 15v (assuming redtop) http://www.optimabatteries.com/en-us/support/battery-care/charging/ so voltage is within the acceptable limits. Quote Link to comment Share on other sites More sharing options...
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