Battery Isolator and Switch (another post about them!)

[Foxtrot]

At one point, my Chevy had dual batteries in it. To start, I'm curious to know if this is a factory feature? It is a camper special and the second battery tray and solenoid (isolator) seem to be original from first glance, but I can't find anything that confirms this.

I want to put dual batteries back in and understand the basics of it all, but can't really decide what type of setup will fully suit me. I don't use it to haul a camper. Instead I want to use a dual setup so I never have to ask someone to jump my truck again (headlights get left on every few months) and to power a ham radio or other small electronics (like phone chargers).

What's the best solution for me? Just a battery isolator? Any recommendations for relay-style isolators--I kind of want a specific switch for the dual batteries, but it's not necessary I don't think?

You've got an empty battery tray in your truck, a disconnected old relay, a ham radio and a habit of leaving your lights on once in a blue moon. What do you do?

[tucsonjwt]

My 83 camper special did not have dual batteries. I installed a second battery tray and battery and have it hooked in parallel directly to my primary battery. I have two start batteries because I have a BB 454 and it has heat soak, so I wanted extra amps for starting when the engine was hot.

I have not had a good experience with battery isolators. Mine only lasted about a year until they failed. I have read online about better quality isolators that last longer, but they are about $150+ as I recall.

I had dual batteries and an isolator on my 73 454. I would jump the secondary battery to the primary battery when that truck had a heat soak - no start condition. After that isolator failed and was replaced twice, the mechanic working on it installed a push button on the dash that would engage the secondary battery and start the truck in a heat soak - no start condition. Otherwise, both batteries were charged off the alternator equally. That was probably the best set up for me.

[tucsonjwt]

I got my second battery tray from LMC many years ago and, as I recall, it was not cheap. It was not a good fit, but I was able to tweak it and make it work. You can get battery trays off ebay that are supposed to be epoxy coated.

If you decide on dual batteries you should get two new batteries at the same time, since the older battery will run down the new battery, unless you do have an isolator.

I now get my Interstate batteries from Costco - about $90 each for our old trucks.

Also, I recommend installing battery mats which you can also get on Ebay. You will need to remove the battery mats and clean them off periodically, but they do capture battery crud and slow the rotting away of your battery trays. They are like a dense felt material.

[wilkin250r]

There are a few different ways to do it, I like the isolators myself.

Just hooking up two batteries in parallel is definitely easy, but doesn't buy you a whole lot. It just acts as one big battery. If you leave your lights on, it will drain both (it just takes longer), and you will end up with a car that won't start.

You can get fancy and add a switch along with your isolator, so your "jump start" is just the push of a button, or turn of a switch, and you wouldn't need actual jumper cables or anything like that.

[Foxtrot]

Thanks for the replies.

I already have the second battery tray (actually took it out when I got the truck) and it fits the truck perfectly, but then again there are like 50 spots this thing would fit perfectly with all the room under the hood. Coincidentally, I have a costco battery in there currently (and love using Costco for batteries/tires), so I'll definitely be getting new ones from them when it comes time.

As for connecting them, it sounds like these are my options:

1) Connect them directly in parallel, in which case I still run the risk of killing my batteries.
2) Get an isolator and use jumper cables when one battery is dead OR add some wiring and a switch to achieve the same effect.
3) Spend a lot of money on a nice isolator with a relay for jumping.

I need a little bit of a knowledge check as I've noticed a few different types of isolators without any extra fancy bits like a switch.

The first kind of isolator has two posts and simply prevents power from flowing backwards from an aux battery to a main (used in ambulances).
The second kind has three posts, one for each battery and one for the alternator which keeps the batteries separate at all times. I could use this kind to install a switch myself to jump the batteries on demand.
The third kind has four posts. Two for each battery, one for the alternator, and one for an ignition lead which keeps the batteries isolated whenever the car is shut off thus always jumping the batteries whether needed or not whenever you turn the key.

Am I correct on all that? If so, the third kind would be the obvious option for me, but I could probably save some money with the second kind and a switch to jump (which I would actually prefer, I kinda like having a few extra switches in the cab for people to ask "what's that do?")

I could probably meander on down to O'Reilly and they'd answer these questions, but I like the collective knowledge here.

[tucsonjwt]

I can't remember what the exact set up was on my 73 (after multiple isolator failures) but I think it involved a relay that would transfer power from the secondary battery to the primary battery when I pushed the button on the dash. Both batteries were charged equally (except for the voltage drop due to the additional battery cables connecting the secondary battery.)

As I recall the principle of isolators, the primary battery gets charged until it is fully charged, then the secondary battery gets charged. So, if you don't drive your truck a lot, then the primary battery will be charged but the secondary battery likely won't have much of a charge. So, when you want to use the secondary battery to assist the primary battery (as in jump start), the secondary battery would not be of much help. Like I said, I had no luck with isolators, perhaps because I never drove the truck enough to charge both batteries. Isolators are intended for RV use, where the vehicle is driven down the highway a lot and that allows enough time for both batteries to charge.

For me, I just joined the two batteries together in parallel which gave me more amps to overcome my heat soak condition.

I would defer to others posting here who understand auto electrical. If you have a good auto electrical shop near you that would be your best source for information. If you do go the isolator route, make sure you buy a good one.

[dieseldawg142]

i'm with tucsonjwt
i've had 2 isolators fail in my crew, both brand name. i too now run them in parallel. it does take alot of juice to fire a 454 in 30+ or -10 weather. i run dual 1000 cranking amp marine battery's in my truck. i can leave the lights on forever if i wanted too. i also installed a cheap manual disconnect for when i have the camper on the truck. only one battery will power the camper so i have a good one for starting the truck

[Tom]

^This is the answer. Im putting a 2nd, deep cycle in my 98 for this summer so I can leave my stereo on at the lake. I'll leave the deep cycle disconnected while the truck is on and disconnect the normal running battery while the truck is off. Never have to worry about an isolater going bad.

[tucsonjwt]

Just one comment on the parallel two battery setup. I find that the secondary battery will not have as great a charge as the primary battery. I think that is due to the voltage drop of about 6 feet of battery cable connecting the secondary battery.

[dieseldawg142]

actually the charge should be almost the same.
even when the vehicle is not running, the battery's will move power back and forth untill their pretty much at the same level.
only downside to running parallel, when one batt goes, 9 times out of 10 you will need 2 new ones. if you replace one, it will dis-charge or damage itself trying to equalize the power in the older battery. one of the reasons i went with marine batts (plus lots of connectors to hook all your electrical junk too...)

[homemade87]

Originally Posted by dieseldawg142

actually the charge should be almost the same.
even when the vehicle is not running, the battery's will move power back and forth untill their pretty much at the same level.
only downside to running parallel, when one batt goes, 9 times out of 10 you will need 2 new ones. if you replace one, it will dis-charge or damage itself trying to equalize the power in the older battery. one of the reasons i went with marine batts (plus lots of connectors to hook all your electrical junk too...)

This is true . One battery will kill the other . No need to use isolators anymore . Marine has move away from them . There is a switching device now that reads the charging voltage and combines the batteries to charge . Isolators burns about one volt . So the second battery had a slower charge rate . Most likely the reason some are seeing weak second battery .The combiner does not do that and supplies full voltage to both batteries . Isolates the battery when truck not running. This device has proven to be reliable . Could add one of these and the battery terminal switch ( shown above ) to the second battery for a jump and be in good shape .

Its not a good idea to leave 2 batteries hooked together all the time . All it takes is one cell in one to go bad and it will drag the other down . This problem mainly occurs when they sit idle and not being charged every day by driving and charging .

Heres some https://www.bluesea.com/products/cat...harging_Relays

[wilkin250r]

I agree with the above posts, in theory. If you connect both batteries in parallel, one bad cell can (and often will) kill both batteries.

However, I disagree in spirit. You run nearly the same risk with one battery. One bad cell, and you're stranded. One might argue that "twice as many cells means twice the risk", but is it REALLY all that risky? The vast majority of my batteries have died either from neglect, or just old age. Very rarely do I have a perfectly good battery just die on me from a bad cell.

So I'm taking a very small risk, and doubling it. Leaving me with... still a very small risk.

[tucsonjwt]

Aside from the battery science thing, I have found that whenever I check the state of charge of both batteries, the primary battery always has the greater charge, often by as much as 20% more. Both batteries were purchased at the same time, and there is nothing different between the two batteries except that the alternator charges the primary battery directly, and the secondary battery gets its charge via the long battery cable.

I do have a higher output alternator (I think 140 amps), but I don't think that makes a lot of difference. I suppose charging two batteries instead of one battery might lead one to want a higher output alternator, and that is supposed to require bigger wires to/from the alternator.

[Tom]

Originally Posted by wilkin250r

I agree with the above posts, in theory. If you connect both batteries in parallel, one bad cell can (and often will) kill both batteries.

However, I disagree in spirit. You run nearly the same risk with one battery. One bad cell, and you're stranded. One might argue that "twice as many cells means twice the risk", but is it REALLY all that risky? The vast majority of my batteries have died either from neglect, or just old age. Very rarely do I have a perfectly good battery just die on me from a bad cell.

So I'm taking a very small risk, and doubling it. Leaving me with... still a very small risk.

Pretty sure most people go with a second battery as a backup for leaving a light on, stereo on too long etc, not for cell just dieing on a road trip or what not.

[GRADYS Performance]

You could trying a solenoid used in RVs that only use power to turn on or off and do not need power to maintain position. They are called clamping solenoids. that way they do not draw power to keep the circuit open or closed.

[Foxtrot]

Lots of great feedback. Here's what I think I'm going to end up doing (feel free to share your thoughts)...

I'm going to get a solenoid relay isolator (or whatever it's technically called), maybe this one.

I'll hook each of the batteries to their post, ground the one post, and the final post which normally is hooked to any "on with ignition" I'll do just that but add a three-way switch. When the switch is in full-off it will disconnect power to the relay and isolate the batteries. The other two switch positions will connect on "on with ignition" power supply (so that in that position operation will be "normal", batteries connected when the engine is running) and the final will be connected to a supply that is ALWAYS powered so I can override and force the two batteries to connect (I believe this is what you can call "emergency power")

Does that compute or am I hair-brained?

I'm thinking I'll go this route because
- Solenoid isolators are MUCH less expensive for higher amperage
- Will not cause a voltage drop (a bit important for the more sensitive elctronics I plan on powering--ham radio)
- Many of these solenoids (though not the one I linked to) have warranties for a few years or guaranteed to last "100,000 On-Off cycles"
- This way gives me the control over things and an excuse to add a new switch in the cab. (though admittedly this isn't necessary).

[jjmorrse]

If you have spare space for a bracket, you could run both a 2nd alt and battery, and have redundant charging systems. If you need a jump, just use jumper cables. Can then have more dissimilar batteries too.

[Foxtrot]

Originally Posted by jjmorrse

If you have spare space for a bracket, you could run both a 2nd alt and battery, and have redundant charging systems. If you need a jump, just use jumper cables. Can then have more dissimilar batteries too.

I like this idea, and would cut out having to use jumpers by installing a switch (or ironically, a relay) to jump them on demand.

Once the weather clears up a bit (or is at least warmer) I'm going to delete the AIR pump which will leave me a spot for an alternator right below the alternator.

How practical is it though? Especially considering the extra investment, weight (not that I'm chasing grams), drag on the engine, etc.

[Tucson38]

You are probably referring to a post I started about a week or so ago on this topic. I received some great information and here's my take: Like you, I wanted primarily a system allowing me to self rescue a dead starter battery. I decided to go with a 150 amp Battery Doctor VSR isolator. The VSR style has little voltage drop compared to the diode style isolator. If your primary battery dies you can push the override button on the unit and essentially transfer power to your starter battery. This system also allows for the use of accessories such as a winch or something. The cost of the unit is around $75 or so, a reasonable price from my perspective. Hope this input helps, good luck on whatever you choose to do.