Hey All
Just wondering why I NEED a battery tender? I can see over the winter, Im not running my car for weeks maybe months at a time but this time if year if I run her every- every other day Im fine. If I let it go more than a week it seems my battery drops to about 11.5 V. What is the draw? radio, security, something else? or does the battery get "addicted" to the Tender ? I would think not but Ive had other cars that could go a week without being started that have never been on a Battery Tender... thanks for any thoughts.
P.S. Its raining today here and this is something Ive been wondering for a while....board...

 

Only time I use one is if the car is not going to be started for a month or more

 

For the first 5-6 years that I had my tender that was the way I used it. for the past year or so Ive needed it over the summer also if I dint use the car for 7-8 days. could it be my battery is just going bad or is there some draw I dont know about? How would I find the draw ? If I disconnect the battery and hook a meter up will it show a draw?

 

mine had a draw inside the starter ...got a new starter and no moore need for a battery tender .

 

Some like a battery tender, I personally have a cutoff on the negative battery cable. In addition to no parasitic battery draw it pretty much eliminates the chance of an electrical fire in the car when not in use.

Just my thoughts.

 

How old is the battery ? It could be on the way out if it is ~5 years old. If you do find a draw you can go fuse by fuse to isolate what circuit it is in.

 

Since you're bored, let's start with "bored" vs "board"!

My 89 has the same symptom and has forever. The alternator shop says it's normal of many cars that sitting for one week (or more) can draw down the battery. I'm not so sure batteries don't tend to drop just sitting. That aside, 1980's electronics wasn't as efficient as it's getting each day. Even when "off", there are some live circuits pulling juice from the car. Mostly memory things like the computer, radio, etc...

It's interesting that a starter could pull voltage. I'd wonder if the solenoid wasn't fully disengaging? Anyway, I suspect the general consensus is it should sit longer than a week w/o significant drop. Probably the best way to isolate the circuit/component would be to remove one fuse each time you park it for a week. Or...use a volt-ohm meter to find current draw leveraging the fuse panel.

Battery tenders aren't terribly expensive AND they can be setup with a quick-release. That may or may not be the easier option depending on how bored you are.

 

Bored..oops... spell check cant help me with that one..lol
The battery is about 6 years old since I only put around 1000 a year on the car Its easy to for get things like that don't last forever. My starter is only 6 months old and the problem is older than that so I can probably check that one off. My engine is heavily modified I dont believe ECM is controlling anything at this point but is still hooked up. all sensor wires oh harness have been capped off the only added electronics are after market stereo and amp which I know turn off with ignition (no clock) . Its not a pin to hook to tender, I have it hung from ceiling over the car and the quick connect hooked up. I was just wondering how common this was OR maybe even if the tender was making the battery more dependent ...some how..
maybe I should just go surfing since Im Board...lol

 

6 year old battery...start there

 

Original batteries are usually pretty good, but I wouldn't trust an aftermarket one after 5 years.

 

Load test time.

 

Funny how time flies.. If you put this battery next to my 3 yr old daily driver you would pick this one. I do detail under the hood all summer long. I wonder how long I should just keep it on the tender before buying a new one? For now it does perform fine as long as I hook it to the tender when Im done a run.. I usually dont drive it anywhere. just out for rides then back to garage or driveway to "tincker", clean ,detail ect..
thanks to all for all your replies. Ive been checking connections today and all looks fine. new alternator also.. Fun day all in all. bad waether for the boat so it was nice to spend some time with the vette... to all

 

While you certainly could start by replacing the 6 year old battery - might I suggest a bit of detective work would be appropriate.

Find an inexpensive digital meter that can measure DC current (sometimes you can get a free Digital Meter from Harbor Freight with a coupon and a purchase). Then fully charge the battery, and then disconnect the neg battery cable. Then put the Digital meter in current measuring mode and connect one lead from to the neg terminal of the battery and the other lead to the disconnected batt lead. This will allow you to measure the current draw with the car just sitting there (sometimes called the static current draw). Now - it's not uncommon for certain computers in the later C4's to wake up as power is restored - so wait 5 minutes for the to "go back to sleep" before noting the current flow.

I can't speak for all C4's - but the LT1 cars typically pull between 20mA and 50mA when sitting.

So - if your battery has a 100 min reserve capacity - that means that the period of time that a battery can supply 20 Amps without the voltage falling below a certain level (I believe it's 11.5 Volts) is 100 min. So - a 25 mA draw would mean that the 100 min reserve capacity battery could supply the 25 ma current for roughly 70 days and still be able to start the car....

If the current draw is on the order of 25mA to 50mA - I would think that replacing the battery would be the next step... If the current draw is higher - you should probably figure out what's drawing the excess current. Pulling the fuses one by one and noting the current draw difference is a good start - but remember - not everything on the car is powered through the fuse paned (e.g. the alternator and the starter)...

 

I just purchased my C4. While inspecting it I noticed the battery was 7 years old. It wasn't having any issues the car was starting quickly it seemed like a good battery. So I replaced it. My rationale is that this car is not easily towed. Changing the battery on this car is not something I want just any idiot trying to do. I'm a fairly young guy but my tolerance for breakdowns and roadside maintenance is quite low. When batteries go they tend to go by surprise. A hot summer day and you go out turn the key in the mall parking lot and nothing happens. If you are a healthy guy that is willing to tolerate a little parking lot maintenance then there you go. At 7 years the writing was on the wall for me and I took the time to read it. It's really a personal choice for you at this point.

 

If you doubt your battery is good or just not sure, take if over to Napa, they will check and load test it. This is the key, does the battery give enough current? If not, time for a new one. Likely other parts places do this too.

I took one to Napa thinking I needed a new one, was just coring it right away. They grabbed and load tested the old battery. It checked green, they said I didn't need a new battery. Think about that, a battery seller passing on a sale just because what you have is fine? Hard to find these days.

 

Simple. ALL newer cars have power draw while 'off'. From radio presets to keeping GPS (some units) ready for the near-instant use we demand. My 50's era vechicles can sit for months and still start w/o tender or jump.

Two specifics: BMW was sued by an AL lawyer when his 8-series was dead with a week of no use. One result was their adding a 2nd battery to the car.

Having owned the electrical nightmare 745Li, with an incredible amount of battery issues. emerging as troubles with everthing from HVAC fans speeds, to progressive shutdown of the car's systems, even with daily use! The integrated GPS system was kept in two standby modes, time dependant. For instant use of these devices, they need current satellite data, which requires power.

Add all the other devices we optioned to casr; most require 'off' power, just as any new televison is never really OFF.

The key is what is normal drain, listed above and measured with a simple DVOM's current probe; in series, battery (+) to cable. My Shinoda Vette sits for long periods and has a permanently mounted NAPA tender; the closest I intend to get to a plug-in car for some time!

 

May I add one more situation, from the alien planet I seem to reside upon. A quality tender on a '99 MB in Alaska, that sat for months. A couple years ago, I attempted starting it but found the battery had been cooked dry. The only reason I could muster was the ML430's standby parasite drain triggered the tender to constantly charge that new, and very expensive, MB brand battery. The solution was battery disconnect with tender operating, albeit minimally. Months later, all was good.

 

Old battery on a tender = hospice, get a new one.

Suggest a charger that automatically switches to "maintain" mode such as a Shumacher.

 

All chargers are not created equal. I believe the cheap Harbor Freight version is actually just a trickle charger which never turns itself off. It is marketed as a float charger but from what I have read it never cycles. Not cycling leads to that empty battery mentioned earlier. I purchased the "Battery Tender" brand that Walmart markets and I have been very happy with it. Prior to getting it, I went through 2 Shumachers that never worked like they were supposed to. They were really bad about overcharging. My little Battery Tender light turns green and the next day when I check the voltage I get 12.7 volts...perfect.

 

^this was my thought.

You should be able to go at least a month without any issues starting the engine. It's easy to get the battery tested so that is what I would do first. If it tests good, find out where the draw is coming from.

Also I would disconnect the battery leads before attaching a tender/charger, even if it was designed to be used while the battery is hooked to the car. Battery tenders and chargers should only be need during long-term storage during which the cables should be disconnected anyway.