rmcquet

(Edit: Didn't use the search function before posting. Looks like there's a ton of useful info on this out there already, so feel free to disregard.)

New to me '89.
Prior owner said "Make sure you drive it every 10 days or so at least, or the battery will die".
Ok, sounds a little odd, you would think it could sit for longer than that and not be a problem.

Well, I go on vacation for a week and change, come back, turn her over, and dead as a door nail. I'm talking not even a single light goes on. Nothing. No clicks.

So, three questions: what is the best battery to buy? Probably going to just go ahead and replace the current one (will also give oppty to clean out the battery tray).

Second: does anyone use a trickle charger? If so, best kind?

Third (and most important, I think): Any guesses on what is pulling from the battery? It has what I think is an aftermarket alarm system that may be the culprit, but I know nothing about where it is hooked up, or how it works. Going to look into it this weekend. Any similar probs w/ alarm systems?

UberXY

I only drive my 911 about once a month and it always starts fine, no trickle charger. The battery in it is nothing special - it's an odd size and I had to take what I could get.

I'd find the fuse for that alarm system.

BTW I do use trickle chargers on my motorcycles. I tried various Brand X's for awhile, but in the end I've had the best and longest luck with Battery Tenders.

redridge

in warm weather, battery drain should not be an issue.... maybe you have alternator problem. But the new battery will tell you what is happening.

ron mcatee

I went with an Optima dry cell in my 88 Carrera. It sits sometimes for a month without any charging and starts on 2nd crank. I did have an alternator problem and fixed it, then added the Optima to get away from the acid. I also found my radio was partly to blame. The memory side of it had shorted to the battery/switch side and that allowed for the current to be on all the time. Probalby not your problem, but you never know. As stated, it may be the after market alarm system.

theiceman

my money is on the alarm .. charge current battery .. put ameter between positive post and battery cable with the ignition off ( so you can see what current is running THROUGH the meter ) shouldnt be more than about 15ma. me thinks it is way more ..

start pulling fuses till it drops drastically . then you have the circuit with the drain .. if none of the circuits do it then could be a bad diode in your alternator disconnecting the alternator would eliminate this. to see if it will still turn lights on after a week.

1986 Targa

Before you open up your wallet...........

As suggested, per the Bentley, do a residual drain evaluation.

The residual drain should not exceed 125ma.

With the meter still connected, ignition-OFF, start pulling fuses.

That will show you the culprit.

I have helped several P-car owners with this same problem.

Aftermarket alarm systems are notorious for this issue.

Good luck,

pm me as needed.

Gerry

rusnak

+1 on checking parasitic drain. I have no idea which battery is best. I tend to buy AC Delco Professional batteries. I had one go bad in two years, and got a brand new replacement FREE. I would look for a "float charger" or a smart charger with a float setting.

vracer

Ron misspoke; it is not a dry cell, but a form of AGM. Optima used to be the 'go to' battery, but recently they have had some QC problems (and they don't fit easily).
Do a search, and them get an AGM. Two sizes fit perfectly; the smaller is adequate.

theiceman

oh yeah I use a c-tek charger . Porsche also uses it and rebadges it . I think i have the Ctek 3300. Got it on sale for 30.00. best part is it unclips when you back out of the garage and forgeting to disconnect it .. not that i have ever done that