V_for_velocity

How long will a car battery hold a charge given a reasonable ambient temperature and no load?

How long will it stay viable if the car is undriven but it has to keep the alarm armed, etc. etc. (same temp.)?

Go48

Of course, it depends on the capacity of the battery and the drain on it with the ignition off. The OEM battery in the RX-8 with the spec drain of 20mA should last quite a long time. My guess would be 2-3 months. You can figure it out yourself if you know the amp hour (AH) rating of a given battery and the backup power requirement (i.e., power drain while ignition is off). For example, if your battery is rated at say 50 AH and the backup power requirement is 20 mA (.020 amp) the battery will be completely drained at 2,500 hours (or about 3 months). Of course, the battery will be incapable of doing useful work long before that. Also, I don't know the exact AH rating of our OEM battery, but I believe it is less than 50 AH.

Of course, if there are additional draws created by aftermarket or malfunctioning OEM equipment, the time would be reduced accordingly. One member had a 300 mA draw from a malfuntioning NAV system and his battery was dying within a week.

V_for_velocity

Thanks, old guy. That helps.

Go48

Sure. Stay warm up there!

Nubo

Also, keep in mind that most car batteries don't tolerate deep discharges well. Run them down a couple of times and you've permanently lost a good part of their storage capacity. If you frequently let the car sit for days or weeks at a time you might want to consider a deep-cycle battery such as the Optima Yellow-top. They're built to withstand repeated deep discharge cycles without damage, and they maintain their voltage better into the discharge so it can be half-drained but still do a decent job starting the car.

And if you're gonna let it sit for a month or more, there are gadgets that will let you keep the battery topped off.

portero23

I just found out how long my battery would last... Just about 3 weeks!!! The battery's so dead the locks don't function, and the brake lights take 3-5 seconds before slowly lighting up... I checked and there wasn't a single thing on - no headlamps, parking lamps, map lights, turn signals... No nav system so there isn't that possibility of malfunctioning. One thing that did happen was about 3 weeks ago she flooded and had to be brought in for service, so the battery might have drained down a bit from a couple attempts at cranking. I suspect that's part of the problem, also that it has dropped about 30 degs or so in New England.

Question, are the Optima Yellow Tops optimal for cold weather usage? Thanks... I'm winterizing Alicia this weekend...

-P23

RX-Nut

just about 2 weeks for me.. my baby didnt start after that. strange.