Battery Isolation switch?

[voigtbd]

Son-in-Laws 2003 3500 has 2 batteries that drain to no start in about two days.

I bought him two battery isolation switches.

QUESTION: Should I start by placing them on each positive terminal? Then see what his batteries do after two days?

He's got 4 gauges, Airdog fuel pump and pac brake all pulling power from the batteries. If they stay strong with the positive isolated, then he should start looking for exposed wires or grounds on each of his aftermarket installs??

Feedback appreciated.

 

[AH64ID]

I don’t think you need to install anything. Find a clamp on DC ammeter and see what wires are drawing what.

Exposed wires aren’t good, but they also don’t draw power just because they are exposed.

Do the gauges have a relay that turns them on/off with the ignition?

 

[petersonj]

If you have the time (and it sounds like you do), I would just disconnect the ground wire from each fully charged battery for a couple of days. After a couple of days check the battery voltage. If the voltage is low and the engine cranks slow, then the batteries are the culprit. If the battery voltage is around 12.6 volts and the engine cranks fast, then you know that you have a current draw situation. It will cost you nothing to perform this test and the test will be conclusive.

- John

 

[voigtbd]

John, I'll confirm but think he's done disconnect and batteries were good...they are 5 months old.

AH64 -I'll hit an auto store and get an ammeter to find the culprit line. If you flew Apache's, my hats off to you! Our SEAL units loved having those overhead!!

Thanks!

 

[kthaxton]

Are the batteries identical and the same age? If not, that could be the problem. If they are, as said, could be a wiring issue or one battery has a fault and dragging the other down.

No need for isolation.

 

[Ozymandias]

You can park that truck for a month without draining the battery's to low to start it.
Sure there is something wrong with the added wiring / gauges.

 

[Matt42]

Are the batteries identical and the same age? If not, that could be the problem. If they are, as said, could be a wiring issue or one battery has a fault and dragging the other down.

No need for isolation.

I had two group 27 AGM batteries from Batteries Plus that were the same variety, but with two different lot numbers and two different manufacturing dates. I knew there was going to be trouble with them eventually, but it took six years. I kept the truck on an Optima brand float charger whenever it wasn't being driven. I won't use Optima batteries any more. (+ terminal on one battery, - terminal on the other.)

You can park that truck for a month without draining the battery's to low to start it.
Sure there is something wrong with the added wiring / gauges.

When I took delivery of my truck in 1996, it came came with a dealer-installed alarm system with remote unlock. I liked it then and still do. It's still working. But it drains just a smidgeon of electricity from the batteries whenever the truck is sitting. Ozymandias is correct, though. Without the kind of drain my truck has, good, properly matched batteries should hold their charge for a month. Newer trucks and those with newer entertainment systems may drain more electricity to hold their settings than mine does.

I have thought about installing battery isolation switches. I still have not. There are two general types. One type is a complete on-off switch. The other contains a fuse that permits the radio, alarm and so on to continue to work. But starting current will blow the fuse. Only the first type will prevent one battery from draining into the other until they are both dead.

When my six year old batteries got onto their last legs, I disconnected the negative cables from both of them. Then fully charged them using two separate chargers. I measured the voltage, and at the beginning of the test they were within a tenth of a volt of each other. Leaving them disconnected, I let them set for 48 hours and tested the voltage again. One had held good voltage. The other had dropped at least a volt lower. The battery that held good voltage got put to use on my travel trailer's tongue. The bad one, plus a junk battery got traded in on a new pair of AGM batteries. This time I got the same lot number!

 

[GBourne]

It sounds like some of the aftermarket items have been improperly installed and just need to be moved to a relay(s) that is driven by an ignition trigger.

None of the listed accessories should be straight to the battery.