My bride says that my car battery is weak. "It cranks so slow!" she says. 4MUL8R, being an engineer, seeks actual measured data and takes the car to the local Batteries Plus. Battery checks fine. "No worries, dear!" say 4MUL8R. Some weeks later, 4MUL8R parks the Red Sled for ten days while on an RV trip.

The morning after the return, both cars needed to be moved out of the driveway to position the RV for unpacking and cleaning. And, the bride's car starts with alacrity, while the Red Sled won't do anything. Lights work, door locks work, cranks slowly, but no start.

Now, under time pressure to make an 0730 team run, 4MUL8R has to drag out the charger, etc. to get the car started and running. "Ain't nobody gots no time for that!" 4MUL8R fumes.

The Red Sled finally starts, and recharges itself on the way to the run.

Being misled by a "professional" battery tester, 4MUL8R is now searching the interweb for deals on a good AGM battery at a reasonable price. Thankfully he has a discount with a small box retailer through his employer.

quote:

"professional" battery tester

Probably a little hand-held conductance tester. I don't really like these. They tend to miss marginal or borderline batteries and say they are still good. They also only check for charging voltage, not amp output or especially AC/diode "ripple." However, if the new battery still doesn't stay up, there may be a drain somewhere.

The battery may be perfectly fine. You may have a small current draw that over 10 days is enough of a load to reduce the battery enough to make it turn over slowly.

Place an amp meter in-line at the battery terminal and monitor the current draw with the ignition off.

Since the bride's car started up you could check hers for a comparison.

Does it have a fancy keyfob?

I found that leaving my key near the car for a week was draining the battery since the key kept talking to the car.

Well. That was my best guess.

How old a car? A co-worker had a slow drain on his battery.

Turns out the onboard BlueTooth was on full time and drained his battery.

quote:

Originally posted by SpinZone:
The battery may be perfectly fine. You may have a small current draw that over 10 days is enough of a load to reduce the battery enough to make it turn over slowly.

Place an amp meter in-line at the battery terminal and monitor the current draw with the ignition off.

Since the bride's car started up you could check hers for a comparison.

This. It seems something is draining the battery while the car is running.

quote:

Originally posted by SpinZone:
The battery may be perfectly fine. You may have a small current draw that over 10 days is enough of a load to reduce the battery enough to make it turn over slowly.

Place an amp meter in-line at the battery terminal and monitor the current draw with the ignition off.

Since the bride's car started up you could check hers for a comparison.

This ^^^^
If draw is high then pull fuses one by one to find the parasitic draw.

Not always the battery.
I have a new-ish Optima Red Top AGM and thought mine was bad.
Turned out at the time I was doing some car repairs (stereo wiring) and would leave my doors open for hours in my drive way.
Then it would not start, and had to recharge.
It was the draw and learned to close my doors.

Example:

quote:

Originally posted by 4MUL8R:

Being misled by a "professional" battery tester, 4MUL8R is now searching the interweb for deals on a good AGM battery at a reasonable price. Thankfully he has a discount with a small box retailer through his employer.

It's likely you have a drain, which you already know, no doubt.

Lead Acid car batteries need more than a voltage check for state of charge: they need a load check. Pick up a battery load tester at Harbor Freight (they work fine). You should also look at the specific gravity of each cell after the battery is fully charged. Look for both specific gravity within the appropriate range, and one that's significantly different from the others.

It goes without saying that one must ensure the battery is properly serviced, always with distilled water (assuming it's not a sealed battery).

Look for a current draw somewhere in the vehicle that's causing the problem.

Check to ensure that your charging system is adequately charging. Your battery tester can also look at the charging system. The simple check is that you rise from 12 VDC to 14 VDC on the batter positive to ground, or across the battery, as you run the engine.

Take the car to Walmart and get a complete battery load test done. It will take over 30 minutes for the test. Then you will know for sure.

quote:

Originally posted by Elk Hunter:


This. It seems something is draining the battery while the car is running.

If a battery is discharging while the car is running, it means the charging system is not doing its job; alternator belt slipping, bad alternator, failed diodes, or failed voltage regulator, or bad grounds.

Always start with the battery terminals and ensure that the battery is able to get a charge in the first place, if the battery is known to be good. Make sure they're clean and tight, and that there isn't sufficient corrosion in the cables, ends, connections to prevent good electrical contact. Check the negative cable ground end and ensure it's clean and tight.

Make sure the battery is receiving 14 volts with the engine running.

If the battery discharges while running, the battery may not be able to receive a charge: charge it overnight, then check specific gravity.

If the battery is 2 years old, replace it. If it's been discharged several times, replace it.

Modern cars with electronic conveniences have a bunch of microprocessors (mini computers) that draw a tiny bit of current from the battery. Alone, a microprocessor doesn't draw that much but combined with all of the others, it's more than enough to discharge a battery over time. If the car sits for a period of time w/o being charged, the current draw can be enough to discharge the battery. You may have lights or horn but not enough to start the car.

Our Tahoe and Corvette each have about 20 microprocessors. It's what you have to accept if you want all the modern conveniences that newer vehicles come with. While the Tahoe is driven several times a week, the Corvette sits on the lift for 4-6 months of winter. It's always on a BATTERY TENDER PLUS. The device brings the charge up to full capacity (over 14 volts), then goes into sleep mode. Open a door, hatch or put the car into accessory mode and the voltage may drop enough for the device to wake up and charge 1.25 volts into the battery until fully charged, then it goes back into sleep mode.

http://www.batterytender.com/

A regular battery charger puts to many amps into a battery to keep it connected for long periods. That can damage the battery.

FWIW, I've had batteries last almost 10 years using a BATTERY TENDER device, both oem batteries and OPTIMA red top. This is in AZ summer temperatures and northern AZ winter temperatures.

A battery with a bad cell can still show a full charge. The first order of business should be a full load test. That will determine whether or not if a cell is bad.

I got a coupon from Advanced Auto Parts for 30% off one item for an online purchase, which I used to buy an AGM battery for my truck. I then did a second purchase with the same code for the second AGM battery for my truck.

Advance Auto Parts is like Harbor Freight in that there's always a coupon/sale. I had left the item in my cart for awhile and got a pop up that was a bigger discount than the standard one.

quote:

Originally posted by Johnny 3eagles:
A battery with a bad cell can still show a full charge. The first order of business should be a full load test. That will determine whether or not if a cell is bad.

A load test will determine capacity, but only by testing each cell for specific gravity will a bad cell be positively identified.

If the battery is load tested, a low capacity does not necessarily point to a bad cell, but may be the overall battery condition; it's necessary to open each cell and check, after the battery has been charged, for the correct value in the electrolyte.

If the battery is fully charged and will only output a voltage below rated (eg, 10, 8, etc), it may be one cell. It may also be several cells with diminished capacity. This isn't uncommon when the battery has been serviced with tap water, has been allowed to sit for a time, or has been discharged several times.

I have a 1953 Dodge M-37 that has no modern things that draw current while turned off. 24 volt system with a generator. If I don't drive it for a few weeks, the batteries don't have enough juice to start the truck. I put a kill switch in and now it works fine. I don't know what is draining the batteries, but something surely is.

I side with those who are looking at a parasitic drain. And a full load test is a good idea, too.
I have a 2018 Silverado. Loaded with electronics. I make it a point to start and run it for a few minutes if it has been parked for more than 24 hours straight. I start it every day in winter. If I am going on a trip for more than three days, I have my cat sitter (trusted) start and run the truck while I am gone.

Just ordered the Battery Tender Plus for my S2000. I can start it up with a booster pack, but prefer to have the battery kept charged.
Thanks for the recommendation!
SigForum: solving my real-world problems, one at a time.

My GTO has a parasitic draw that has gotten worse over time. It takes less than 24 hours to draw the battery down to where it will no longer start. I haven't been able to track it down yet, so every time I get out I disconnect the battery. It's a pain in the ass, but it keeps me from being stranded.

quote:

Originally posted by Perception:
My GTO has a parasitic draw that has gotten worse over time. It takes less than 24 hours to draw the battery down to where it will no longer start. I haven't been able to track it down yet, so every time I get out I disconnect the battery. It's a pain in the ass, but it keeps me from being stranded.

How old is the battery? A load that's attached to the battery shouldn't be increasing; a load is a load. Your battery conditions sounds more like it's deteriorating (do a load test, check specific gravity after a full charge), it's not getting an adequate charge (clean connections, check alternator function), or isn't serviced (check fluid level).

Any time a problem increases and gets worse, it's a sign of inadequate charge or a bad battery, progressively it's often both.

It's a wise idea to put a battery disconnect in place if there's a known draw on the battery when not in service. There are various versions. I have one on the truck that's just a switch; raise the handle to disconnect, put it back in place to restore the battery. Far better than removing the terminal connection at the battery each time.

Check your terminals and connections are clean and bright, and your negative ground is clean. If the battery is approaching two years, replace it. If it's been discharged several times, replace it.

 
We have Battery Tenders on everything that does not get driven every day, and they are set up and ready to be used for those vehicles as well. The BT's not only keep the charge up, they will extend the life of the battery by keeping sulfation down.