My rx8 has been off the road for 6 months for the winter. Battery has been in the house on a battery tender. Testing it with a multimeter it read 12.95 volts. What I noticed was as I held the meter on the terminals, the voltage dropped .01 volts every second. It kept dropping to 12.70 volts but started dropping more slowly every few seconds. As I held it longer it dropped to 12.49 volts but took about 20 seconds to drop every .01 volts. It probably took a total of 2 minutes to go from 12.95 to 12.49. Amy ideas? Bad battery? Multimeters use a lot of power? I'm thinking this last statement can't be possibly true....can it?

 

If the multimeter used that much of a full battery you would find yourself holding a small sun with wire probes. Either heat affects something in the multimeter and throws it off, or the battery has lost all of its capacity.

If you retest it again, is it still at 12.49 or back at 12.95?

 

It's been an hour and the battery is at 12.32. Time for a new battery. It was a 3 year old Die Hard. Guess they don't make them like the old days.

 

Overnight it held at 12.30 volts. Yes or nay on a new battery?

 

Drive to an automotive store that sells car batteries and ask for a free load test. That will answer your question and will give you more info than a multimeter will tell you.

 

Volts don't cut it for assessing battery health. Several items do: (1) as mentioned above - get a load test, (2) charge it using a smart battery charger (which will sense voltage gain under load) and alert you accordingly, (3) recognize that a 3-yo battery stored in the normal RX-8 engine compartment driven often and that's hotter than H@ll has a life expectancy of...3 years, (4) find the curve for your specific lead acid battery and watch the voltage (static/not connected to anything else but the charger).

My previous Interstate burned me in year 4 and my current Costco Interstate battery is on year 3.1. Guess what I'm doing this Summer before a long trip?

 

Thank you fellow RX8'ers.