cal7380

Due to my infrequent driving, when I garage my car, it is on a trickle charger. Of course, it always starts up strongly. But, how would I know if my battery is nearing end of life, so that if I go away for a weekend trip and the car is not connected to the trickle charger, it will start OK after sitting in a hotel parking lot overnight?

Thanks for your input.

Cal

DanL993

Get a volt/ohm meter, preferably digital, and monitor the battery off the charger while it sits over the weekend (or for however long you need to test/monitor). Check it two to three times a day and note the voltage. Then see how strongly it starts after the test.

I did this when I thought I had a parasitic problem. Battery should stay up around 12+ volts. If it leaks down much past that, you may want to replace.

IXLR8

By performing a load test and capacity test. Those are the only methods of determining a battery's true state of health.

Your battery's open circuit voltage (battery disconnected) should measure 12.65 to 12.85 V when fully charged. That reading is taken about 8 hours after charging has been performed.

You can also measure the current drain using a meter. It should be well under 50 mA with the security system set.

Stealth 993

How about you just leave the charger off the battery & see how long it last in the garage?

IXLR8

That'll depend on the standby currents.

Even a good battery will self discharge over time...disconnected...about 0.01V per day for a conventional FLA battery and much less for an AGM battery. If in higher temps (Arizona for example), it'll self discharge far quicker.

Stealth 993

Yea, but a bad battery will be dead in a matter of days. While a good battery will last weeks, or months.

IXLR8

One still needs to know what the current draw is. Just because the battery drains in a matter of days does not mean the battery is bad. The car may be draining the battery at a higher rate than expected if there is a current drain higher than usual.

My battery that I replaced last April was bad. With a draw of 22 mA, the voltage was dropping far too fast...an indication that capacity was't all that great anymore.

Even though it started tha car, I am glad I replaced it. I would never have made it home after the alternator belt broke some 100 miles from home.

BTW, I ended up with an East Penn battery...identical in every respect to the OEM Porsche battery except for case color.