I have 2 large 100aH AGM batteries in the rear and a factory sized AGM under the hood. A cpl weeks ago I went to start the van and it was dead. I got it started and voltage was terribly low. I only ran it for a few minutes then let it sit, restarted a few times for a few minutes...I dont have a charger. After a couple days everything seemed back to normal. I watch the factory gauge a lot closer and am surprised at how much voltage can change day to day while running, independant of hot days to cold days. Some times it runs around 13.5V other times 14.2V, even in the same day, sometimes 14.2V when its warmer and been driving and sometimes 13.5V when its colder and/or less drivn, but vice versa as well.

Today it was low to start, but later it was high, so I disconnected the rear 2 batteries I tested right away, let it sit for 2 hours, tested again, and will keep testing through tomorrow.

Right away Rear Batt 1 was 12.15V, rear batt 2 was 12.03V, front batt was 12.03. I went out and tested again now front batt is 12.03 still, rear 1 is now 11.96, rear 2 is 11.86.

I expect they will slowly keep dropping over night

if your using the alt to charge your battery when its low. It fast charge your batterys which means it will have a faster discharge rate. Get a 2 amp trickle charger and see if your voltage is stiffer

if your using the alt to charge your battery when its low. It fast charge your batterys which means it will have a faster discharge rate. Get a 2 amp trickle charger and see if your voltage is stiffer

Exactly.

Your alternator is not a charger, you're going to kill it using it as one. You need a real battery charger.

trust me.. ANY AGM battery, regardless of capacity(which is good practice for safe operation) that is resting at 12.6v or lower needs to be COMPLETELY disconnected from car and charged via AGM battery charger.

No if ands or buts.. trust me on this.

An alternator is a MAINTAINER, not battery charger.

Alternator is suited to maintain the charged capacity of your batteries installed.

If it tried to be used as a charger, the Bridge Rectifier inside if worked for too long can overheat and start burning out diodes...

If this happens.. u are done... seriously.. alternator slowly dying... So don't do that.

If u need advice on a good charger, let me know.

Sears sells one locally for around $90 that i personally own that works GREAT!

It will be a while before I can afford a charger, $90 is a good way toward the $150 brackets I need for the 2nd alt. Rear 1 is now 11.95, rear 2 11.75, front 12.00VSo keep the rears disconnected until I can get a charger?

YES, and imperative that u understand the following-

While disconnected... if these batts keep dropping.. no charger will help..

Batts that keep dropping have at least one bad cell and any batt that has any bad cell(s) needs to be discarded immediately...

Sorry, but i'm only trying to save you money..

It may not seem like it if ur batts will or are doing this but no good batt continues to drop rest voltage unless it's bad...

Thank you very much for your help, Id rather save damaging more equip down the road. Ill keep disconnected, and keep testing.

after sitting over night R1 is 11.91 and R2 is 11.51

after sitting over night R1 is 11.91 and R2 is 11.51

Disconnect the batteries from the vehicle and charge them with a proper AGM charger. From there you can load test them to determine the condition of the batteries.

As stated the alternator will not perform properly with batteries are not performing to spec. Don't kill your alternator with bad batteries.

It may be time for new batteries, these may no longer be up to spec.

OR you may have a draw on your vehicle causing them to drop overnight when connected. You should check that too.

It could be a draw as Mechman stated. My cadillac had a very small draw and nontheless it killed 3 batteries. But I couldnt find the draw which sucked.

Finding the draw is not as hard as you would think. It can be intimidating with all of the circuits involved in a modern car, but you just apply a little logic.

Hook a meter that can read the amperage of the draw in line in the positive cable. Pull fuses until the draw goes away. The fuse that you pulled that stopped the draw will contain the problem. Once you isolate that circuit hook into the lead out of the fuse and measure the draw. Disconnect everything one at a time on that circuit until the draw is eliminated. The last device you disconnect or the circuit to that device is the problem.

This is a VERY generalized method of isolating electrical problems, this is the most basic explanation so anyone with a meter can isolate the problem and have success fixing their own electrical problems.

It's not hard, just think before you act so you don't damage anything.

Finding the draw is not as hard as you would think. It can be intimidating with all of the circuits involved in a modern car, but you just apply a little logic.

Hook a meter that can read the amperage of the draw in line in the positive cable. Pull fuses until the draw goes away. The fuse that you pulled that stopped the draw will contain the problem. Once you isolate that circuit hook into the lead out of the fuse and measure the draw. Disconnect everything one at a time on that circuit until the draw is eliminated. The last device you disconnect or the circuit to that device is the problem.

This is a VERY generalized method of isolating electrical problems, this is the most basic explanation so anyone with a meter can isolate the problem and have success fixing their own electrical problems.

It's not hard, just think before you act so you don't damage anything.

Mechman that helps a ton! When i did my initial post about this a few weeks back I was assuming it was a current draw, and I had no idea where to even begin. This would make a nice sticky under electrical.

Finding the draw is not as hard as you would think. It can be intimidating with all of the circuits involved in a modern car, but you just apply a little logic.

Hook a meter that can read the amperage of the draw in line in the positive cable. Pull fuses until the draw goes away. The fuse that you pulled that stopped the draw will contain the problem. Once you isolate that circuit hook into the lead out of the fuse and measure the draw. Disconnect everything one at a time on that circuit until the draw is eliminated. The last device you disconnect or the circuit to that device is the problem.

This is a VERY generalized method of isolating electrical problems, this is the most basic explanation so anyone with a meter can isolate the problem and have success fixing their own electrical problems.

It's not hard, just think before you act so you don't damage anything.

This is frustrating. I thought everything as fine but today it was way down at 12V or so running. When i disconnect the rear batts, the front seems fine, and the rear batts hold steady once they settle. So the front one holding steady by itself implies no current draw. The rear batts holding after settling implies they are fine. The only things connected to the rear batts are the amps and crossover. I can't see the amps causing current draw while they are off. It only seems to be a problem when the rear batts are reconnected.

For now I pulled all remote wires to the amps...all on 1 fuse.

I only have a DMM. Will that work for finding current draw, or do I need a clamp?

If your meter has an amperage function then you don't need a clamp.

Emen with the remote wires disconnected oyu could have the amps drawing power, especially if you have amps that have an auto-on feature.

Best simple explination ive ever seen on hunting electrical problems. Good shit MECHMAN

@kryptonitewhite where are you located(im on mobil so i cant see)?

Don't allow a lead acid 12v battery to rest under 12.6 volts because when a battery discharges it sulfates and if you wait too long the sulfation will become more and more of an insulator to the point the battery becomes more difficult to recharge. Try dumping too much power into a sulfated battery you are asking to cook a few things and get a bad recharge on top of it. If your battery is sulfated you can bring them back as long as the charger DOES NOT try to do a total high voltage equalization charge which is hard on most sealed batteries. Pulse chargers that are highly regulated to 14.4 to 14.7 volts can work well to bring back batteries in this condition as long as the sulfation has not crystalized.

Sioux Falls SD. Turns out, my toggle switches to my amps that I run off my headlamp used to shut off when the dome light shut off after closing the door... one of the timer ones that wait 30 seconds then slowly fade. Now the toggles stay on after the dome light shuts off, my amps ( not the 4 AP30001ds, just the 2 KX850.42, KX650.4, and SX500.2... not near as bad as when the subs were working) stay on all night

Now I get to play pilot to air ststems control flipping switches and more switches every time I get in and out :-P

"Air traffic control, tweets fired up, mids a go, Extremis ready to get extreme... PLAY!"

If your meter has an amperage function then you don't need a clamp.

Emen with the remote wires disconnected oyu could have the amps drawing power, especially if you have amps that have an auto-on feature.

Last night I pulled the fuse that kills my dome light and toggle switches, the stock volt gauge was higher than i have ever seen it... 2 lines past 14V. All day i shut the toggles off when I shut the van off. Seems to have done the trick.

So I looked at my manual, there seems to be 4 maybe 5 separate fuses that have some variation to "head lamp" such as "head lamp relay". I didn't take the time to turn the dome light on and pull each one one at a time to see if each killed it... but I did shut the door and watch the dome light go off but the toggles stay on.

So i got to thinking... the fuse that kills the dome light that I know off, if I pull the fuse and measure the contacts... shouldnt the DMM read 12V when the domelight should be on (door open and 30 seconds after closing) then 0V after I wait a while?

When I push my buttom next to my lights, the ones I depress 4 times to shut the headlights off during the daytime... shouldnt that make for 0V across it as well?

http://www.extendedgmwarranty.com/owners-manual/chevrolet/2001-Chevrolet-Astro.pdf

3 Courtesy Lamps, Glove Box

Lamp, Dome Reading Lamps,

Vanity Mirror Lamps,

Courtesy Lamps

4 DRL Relay, Instrument

Panel Cluster

(This is the one that I pull to kill switches, after pullign this voltage stopped dropping. WTF! DRL Relay is what makes the headlights stay on daytime unless you manual defeat it with the button. The button also shuts the dome light off)

9 License Plate Lamp, Taillamps,

Parking Lamps, Ashtray Lamp,

Panel Lights, Trailer Taillamps,

Front and Rear Sidemarker

Lamps, Door Switch Illumination,

Headlamp Switch Illumination,

Rear Seat Audio Illumination,

TBC Module

14 Cluster Illum, HVAC Controls,

Chime Module, Radio

Illumination, Rear Heat Switch

Illumination, Rear Wiper/Washer

Switch Illumination, Rear Liftgate

Switch Illumination, Remote

Cassette Illumination, O/H

Console, TBC Illumination

15 TBC Module, Headlamp Relay

Dome reading lamps were probably separate from the dome light, but not sure. Headlamp switch illumination? O/H Console should be the same as dome light and dome reading lamps... all 1 piece up front and 1 piece in rear. Headlamp relay?

Anyway, I'll just keep killing the toggles from now on..maybe I'll make 1 toggle for the set of toggles to make things easier.