battery voltage

[rb]

My battery at rest is showing 12.3vdc. Is it good or bad

[Ralph Mowery]

Measuring a battery without a load really tells nothing unless it is low in voltage.

[AndyS]

Andy replies: One can't tell from the info available.... I am assuming you are talking about automotive-type lead acid batteries in the 12V systems....

1) Has it been sitting for 5-6 hours since the last charge cycle ? It takes at least that much time for the "space" charge to dissipate for an idle battery. 2) Terminal voltage as an indication of "state of charge" is temperature dependent. 12.3 is a bit low, but it doesn't mean the batter is "bad". It may mean that the "state of charge" is low and recharging is needed. 3) Your best test is to go and buy a specific gravity tester which sells for two or three bucks at an auto supply section. While SG is also temperature dependent, it is a much better indication of the state of charge. The instrument will have directions on how to interpret the results..... 4) Your best bet is to first measure and record the SG for each cell, and then charge the battery at a low rate, say 3-4 amps, for a day. Then disconnect the charger and measure the SG again. This will let you know if each cell can accept a charge, and how evenly they are charged..... In an automobile environment, it's usually the end cell closest to the engine block that goes first. I'm not sure why, but I've seen this a lot of times... Probly heat.... 5) Check the water level in the battery. If you have to top it up, use distilled water, and don't believe any SG readings for a while since the SG tester will pull the "uncharged" water off the top and not be an indication of the true state of charge until use/vibration/ gassing has caused the water to fully mix with the electrolyte.....

Just a few tips.... If you google on "lead-acid battery characteristics" you can spend a few minutes learning a lot about how they should be charged and measured.

Andy in Eureka, Texas

[Dioclese]

In an automobile while engine is not running, 12.6VDC is considered good/normal for a 12 volt battery.