Battery Tender
Thread Starter
Racer
Joined: Dec 2007
Posts: 262
Likes: 12
From: Montgomery Alabama
Battery Tender
Thank you for looking at my post and perhaps you can answer my question. I have a base 1993 coupe that may or may not have an electrical drainage problem, although not severe. When I first start up the reading is 14.7 but after a few miles it degrades to about 14.1. I think this is normal. My question regards my old (instructions are long gone battery tender. Do y'all leave it plugged in whenever you are not using the car? Constantly? I had one short out and burned the wires and that is why I am goosey. Thank you for any information you can share.
Burning Brakes
Joined: Apr 2017
Posts: 1,053
Likes: 291
From: Farmington MO
I use mine (battery tender) only in winter when car is parked for more than a week. Otherwise nearly never use it. When I do use it, I just leave it plugged in. Claiming no expertise. Don't give it a lot of thought.
Race Director
Joined: Oct 2005
Posts: 11,772
Likes: 177
From: Rolla Missouri
2021 C4 of the Year - Unmodified Finalist
St. Jude Donor '10 thru '25
As long as it is one of the "smart" tenders, it is safe to leave them plugged in all the time.
I've had a Battery Tender Jr. connected to my '96 for 4 or 5 months at a time over the last several years.
Never had any issues with it.
I've had a Battery Tender Jr. connected to my '96 for 4 or 5 months at a time over the last several years.
Never had any issues with it.
Le Mans Master
Joined: May 2005
Posts: 7,362
Likes: 2,281
From: Central Maryland
I've used Schumacher brand tenders for years, leaving them connected all winter long, and whenever the vehicles are unused for a week or more. I wired a cigarette lighter plug to my tender, and just plug the cord into the lighter socket to feed the battery. I have about 12 feet of wire between the tender and the lighter plug, so the tender hangs on the wall of my garage, wires go up and over (hanging over a hook that's dangling from the garage door track overhead), and through the open window of the car. Easy peasy, no fuss no muss, no cords to trip over, and connects/disconnects in a few seconds.
The lighter circuit in the car is fused, and for additional assurance, I used a lighter plug that has its own internal fuse holder. My tender puts out 1.5 amps, so I installed a 3 amp fuse in the lighter plug. That fuse will blow before anywhere near enough current can pass through to damage anything in the car.
I've never had a problem with this arrangement. Works great for me, and I've wired up several tenders in the same way for friends and family.
Live well,
SJW
The lighter circuit in the car is fused, and for additional assurance, I used a lighter plug that has its own internal fuse holder. My tender puts out 1.5 amps, so I installed a 3 amp fuse in the lighter plug. That fuse will blow before anywhere near enough current can pass through to damage anything in the car.
I've never had a problem with this arrangement. Works great for me, and I've wired up several tenders in the same way for friends and family.
Live well,
SJW
Last edited by SJW; Oct 24, 2019 at 09:00 PM.
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
with both. I use the Battery Tender brand tender which is a "smart charger" designed (like some other smart chargers) to be left connected anytime the (car) sits.I leave the tender(s) connected whenever the Vettes sit idle (driven mostly on weekends a couple times a month.)
Modern electronic so-called "TENDERS" differ from simple (old) trickle chargers in that they monitor the voltage and shut off automatically when the battery teaches full charge. This keeps from boiling the battery dry if left on like the old fashioned simple (dumb) chargers used to. And, "smart chargers" are programmed to pulse the battery with short bursts to prevent lead sulfate from building up as is normally the case when a lead acid battery sits idle (primarily in warm weather - not so much a problem when temps get below freezing.)
"Thus endith the lesson!" (Sean Connery in the movie "Untouchables").
Last edited by Paul Workman; Oct 25, 2019 at 05:41 AM.
Racer
Joined: Feb 2017
Posts: 388
Likes: 54
From: Sparta New Jersey
I've been using battery tenders, from various manufacturers, for many years to keep my motorcycle batteries charged through the winter. I've never had a problem, though I must throw in that I take the batteries out of the bikes and keep them in my basement. I leave them all plugged in all the time.
BTW, I suspected a parasitic drain on my '93 as well but, after putting my digital VM on it numerous times, never confirmed it. I DID notice that if I checked the voltage on the digital voltmeter in the dash before I started the car (ignition on but not started) voltage always reads low and the longer between starts the lower the voltage but the car always starts with not problem. I suspect something about the built in digital voltmeter is returning incorrect voltage reading with the key on.
BTW, I suspected a parasitic drain on my '93 as well but, after putting my digital VM on it numerous times, never confirmed it. I DID notice that if I checked the voltage on the digital voltmeter in the dash before I started the car (ignition on but not started) voltage always reads low and the longer between starts the lower the voltage but the car always starts with not problem. I suspect something about the built in digital voltmeter is returning incorrect voltage reading with the key on.
Safety Car
Joined: Aug 2013
Posts: 4,430
Likes: 608
From: Minneapolis Mn
I don't user a battery tender, have not needed one so far. Now I do have a heavy duty battery cutoff in the car and if I'm not using the car for a long time or it's in winter storage I just flip the switch and disconnect the battery. One side benefit to a battery cutoff is there's virtually zero chance of having an electrical issue without a connected battery in the car. During the winter I do start the car and set it up or operating temp and if the alley is clean will drive the car up and down the alley a little.
Some swear by a battery tender, some swear at them. It's your choice.
Some swear by a battery tender, some swear at them. It's your choice.
Le Mans Master
Joined: Oct 2004
Posts: 6,314
Likes: 508
From: South-central Missouri
I've been using battery tenders, from various manufacturers, for many years to keep my motorcycle batteries charged through the winter. I've never had a problem, though I must throw in that I take the batteries out of the bikes and keep them in my basement. I leave them all plugged in all the time.
BTW, I suspected a parasitic drain on my '93 as well but, after putting my digital VM on it numerous times, never confirmed it. I DID notice that if I checked the voltage on the digital voltmeter in the dash before I started the car (ignition on but not started) voltage always reads low and the longer between starts the lower the voltage but the car always starts with not problem. I suspect something about the built in digital voltmeter is returning incorrect voltage reading with the key on.
BTW, I suspected a parasitic drain on my '93 as well but, after putting my digital VM on it numerous times, never confirmed it. I DID notice that if I checked the voltage on the digital voltmeter in the dash before I started the car (ignition on but not started) voltage always reads low and the longer between starts the lower the voltage but the car always starts with not problem. I suspect something about the built in digital voltmeter is returning incorrect voltage reading with the key on.
A consistent draw exceeding 50 mA is excessive. You can cut to the chase by reconnecting the battery cable to the battery, and then testing each of the fused links (you will have to remove the GILL PANEL behind the battery to access the fused links. (Refer to the FSM of details!)
Once you have identified the particular circuit with the excessive draw, then it is a process of systematically testing and eliminating the components associated with that jused link.
Good luck Sorry for the short shrift just now...
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Racer
Joined: Feb 2017
Posts: 388
Likes: 54
From: Sparta New Jersey
To determine parasitic draw, realize you have to set the VOM up to read Amperes. (You never mentioned that, so I have to wonder if you knew that?). Normal C4 current draw is ~25-30 mA (.025 to .03A), when one of the battery cables is disconnected (either will work, but the negative is more accessible) between the disconnected battery cable and the battery post (allowing for an initial surge to pass).
A consistent draw exceeding 50 mA is excessive. You can cut to the chase by reconnecting the battery cable to the battery, and then testing each of the fused links (you will have to remove the GILL PANEL behind the battery to access the fused links. (Refer to the FSM of details!)
Once you have identified the particular circuit with the excessive draw, then it is a process of systematically testing and eliminating the components associated with that jused link.
Good luck Sorry for the short shrift just now...
A consistent draw exceeding 50 mA is excessive. You can cut to the chase by reconnecting the battery cable to the battery, and then testing each of the fused links (you will have to remove the GILL PANEL behind the battery to access the fused links. (Refer to the FSM of details!)
Once you have identified the particular circuit with the excessive draw, then it is a process of systematically testing and eliminating the components associated with that jused link.
Good luck Sorry for the short shrift just now...
Burning Brakes
Joined: Sep 2015
Posts: 1,000
Likes: 114
From: Bang Bang Chicago Illinois
C4 of Year Finalist (stock) 2019
I have been using the Deltran Battery Tender and CTEK MXS 5.0 on both of my fun cars. I did have problem with the Corvette battery and couldn’t figure out why the battery died. It was gone and had to be replaced. I did a search here and found a thread where someone ask if something was left on. I check and found out that a light was left on a visor vanity light mirror. I turned it off, replaced the battery and all was good lesson learned, now I won’t let a two year girl play in the car, she likes to look at herself in the mirror
Here is a video I made showing how to attach a CTEK or Battery Tender for someone on the Focus RS Forum:
Here is a video I made showing how to attach a CTEK or Battery Tender for someone on the Focus RS Forum:
Pro
Joined: Apr 2008
Posts: 502
Likes: 37
From: Pine Barrens New Jersey
Thank you for looking at my post and perhaps you can answer my question. I have a base 1993 coupe that may or may not have an electrical drainage problem, although not severe. When I first start up the reading is 14.7 but after a few miles it degrades to about 14.1. I think this is normal. My question regards my old (instructions are long gone battery tender. Do y'all leave it plugged in whenever you are not using the car? Constantly? I had one short out and burned the wires and that is why I am goosey. Thank you for any information you can share.