SLOW BATTERY DRAIN

30 days is pretty normal for a Ferrari battery to discharge. I wouldn’t leave a new Ferrari off of a tender for more than 4 days.

These cars just have a lot of parasitic draw. Maranello has bothered with optimization on this front.

 

The way I'm reading the original post, the OP is connecting the car to a tender.

But to the engine compartment posts.

OP, connect the tender directly to the battery. Pull the front passenger wheel, remove the battery cover, and install a "tail" (wire leads) from the battery up into the little cubby space where the a/c ports are. Then connect your tender to those leads and see if that makes a difference.

 

Maybe the tender is shot?

 

Got it. Read your initial message wrong.

What tender are you using?

 

My guess - there's too much resistance between the engine compartment posts and the battery to enable a tender (trickle charger) to keep the battery adequately charged.

 

Id be surprised. If it cant handle 3 amps whats it doing with 80 or 90 from the alternator?

 

This is not going to be resolved with internet guess work. Are you equipped and capable or interested to do a little serious electrical diagnosis?
The battery should be load tested and the output from your tender should be tested for starters. Also the car needs to be tested for static parasitic draw.

Also the alternator should be load tested. Alternators in 355 have a very real reliability issue. My rebuilding shop retired off what I paid him over the years rebuilding 355 alternators.

 

The car has a drain larger than the battery maintainer can supply.

 

Did you assume it was weak (through age/poor starting) or did a tech diagnose the issue? Was your old battery on the same tender before?

I don't see an issue with using the engine bay terminals. It just means you can't charge your battery with the battery cutoff switch in OFF.

The engine bay terminals are normally disturbed during engine outs. Did you check the terminals for security? Note that the starter and alternator are attached to the engine bay terminals. I think if you had an issue with these terminals, you'd have other problems.

Note also that the engine bay terminals are attached to the battery bus terminals in the passenger footwell (behind the relay panel) and the battery (and rest of car) is attached to the passenger footwell terminals.

It might be a good idea to invest in a cigarette lighter voltmeter so you can monitor your electrical system.

 

Disconnect the positive, and read the amps by attaching a meter in series. If you see more than a whole amp, start pulling fuses to isolate the circuit that is causing the trouble.

Got a window switch that's sticking?

 

But doesn't that prove my point? 3 amps from the tender might not be enough to keep up with the parasitic drain of the radio, immobilizer, etc, and also charge the battery, or charge it enough. The alternator producing 80-90 amps can.

 

Except that was not your point. You mentioned resistance. You said nothing of a drain. Do you understand the difference?

 

The first thing I would do is disconnect one of the battery terminals and insert an ammeter (set at 10A range) to see if there is excessive parasitic drain. The same measurement can be done if the ammeter is connected to the terminals of the battery disconnect switch (while it is "off", of course).

 

Just a "side question" for you. If you had a dead 355 alternator, who would you send it to for rebuilding? Knock-on-wood mine is currently OK (95 2.7) but it would be nice to know who to turn to if and when. Thanks.

 

I would find a highly reputable local shop. A fair amount of these kinds of places are still around. Rebuilding a Ferrari alternator isn’t different from any other car and OEM parts are available (mostly).

 

Well it looks like I spoke too soon because my local alternator/starter shop seems to have closed

 

Rebuilding a Denso alternator is very easy. The somewhat difficult part is getting the alternator out. After that, it's a 15 min. job if you have the parts ready (easy to get). The special tool required - a good Phillips screwdriver.

 

Yeah, that is the likely route I would go anyway. Hunting down the complete kit (bearings, windings, etc) would be the bigger challenge in my opinion.

 

It's tilting and rotating it to the exact angle it pops out of the subframe. It looks for all the world like it won't fit, and then somehow it just slips out effortlessly (fnarrr).

 

If the car is pulling 3A when it's doing NOTHING, you have a problem, not just parasitic drain...

IMO, nothing before 2000 should need a battery tender.

sjd

 

My '85 308 QV will suck a battery down in a few weeks if not disconnected just on the drain from the clock. Been like that since new.

 

Yeah, weeks, not days.... and not 3A worth. You've traced it to the clock?

How much power does it pull? Have you measured?

edit: consulting the internet, the average car battery has a capacity of 48 Amp-hour (Ah). so that's 48000 mAh (milliamp hours). There's 720 hours in a 30 day period... if i'm doing my math correctly, 48/720 is how many amps you're pulling if you're draining your battery in 30 days.... (.066A, or 66 mA)...which is a lot.