Auxiliary car battery

Joined
Feb 17, 2013
Messages
6,305
Likes
4,643
Location
Buttf***ville, MA
Feedback: 22 / 0 / 0
So recently the Grand Caravan decided to shit a transmission and now I have a brand spanking new Subaru Forester with a manual transmission. Now I have to redo the entire CB and ham setup that I was carefully cultivating on the van. Yay.

One thing that I have never been comfortable with is running a wire directly to the car battery. For one thing, I hate poking new holes in the firewall grommets. In addition to that, I would love to have a backup battery, so that in case of an emergency I could power off it and not drain the car's main battery. Now the subie has an auxiliary lighter circuit with a 5A fuse that goes to the middle compartment between the driver and passenger. I'm thinking that if I stick a 20Ah 12V bicycle/motorcycle battery right there, it should not draw more than 2A to charge, will smooth out the power to feed the ham and cb, and if necessary I can install a kill switch that will power the accessories off the auxiliary battery only.

Thoughts?
 
Look at the Australian off-road folks. They run dual battery setups all the time. You’ll have to do some research about what is required.
 
I've done a few different installs, but pretty much always go back to a direct harness.
Unless I was running a couple of HF rigs or something, I would run a good pair of fused on both ends and both wires straight off the negative frame connection and the positive of either the battery or where the battery POS goes into the fuse box in the engine. Run that to the cab and use Anderson poles to split out.

My last install did poles to a Y. One side went to 2m-440cm dual bander, other side went to a home made switch panel with a volt meter cig plug, and dual 2x USB chargers, each were switched. Everything was fused POS in the driver's compartment. Radio and main cable fused POS and neg. Just in case wires get cut.

If I need any more power than that .(say two 50w radios, or running a laptop as well) I would have ran power through an appropriately sized circuit breaker. The off road shops make some good ones. I think I have an 80 and 120w in my box, but not installed anywhere.

I wouldn't run dual batteries, but I would get a good jump pack and b able to plug into that (hint, Anderson pole quick swap out to a cig plug)

I've never had issues direct powering. Honestly I wouldn't trust any cig plug in modern cars to power RF. It probably goes through the radio, fuel control computer, sun roof and butt warmer circuits and maybe the emergency eject system before you draw off it. If you screw up and your radio toasts, you may kiss all those expensive linked subsystems good bye.

A pair of good 6-10 ga fused (use appropriate everything!) Wires from the power source == no issues. Also knowing the exact voltage before you start the car is sort of nice. You'd be surprised how much it can tell you .
 
Don’t copy any wiring diagram from a not a Subaru Forester.

Grounding back to the starting battery ,alternator , and Hal effect , fuses ,wire melting , must be addressed.

It’s not 1970 under your hood anymore.
 
I have a Wrangler NW Power Products dual batt system in my CJ. Amazing. Three positions: isolate, dual, and emergency. It kept my two blue top optimas running for 16 (SIXTEEN) years. One finally died, retired them both, the other went to work on the back of a snowmobile groomer powering the lights.
 
So recently the Grand Caravan decided to shit a transmission and now I have a brand spanking new Subaru Forester with a manual transmission. Now I have to redo the entire CB and ham setup that I was carefully cultivating on the van. Yay.

One thing that I have never been comfortable with is running a wire directly to the car battery. For one thing, I hate poking new holes in the firewall grommets. In addition to that, I would love to have a backup battery, so that in case of an emergency I could power off it and not drain the car's main battery. Now the subie has an auxiliary lighter circuit with a 5A fuse that goes to the middle compartment between the driver and passenger. I'm thinking that if I stick a 20Ah 12V bicycle/motorcycle battery right there, it should not draw more than 2A to charge, will smooth out the power to feed the ham and cb, and if necessary I can install a kill switch that will power the accessories off the auxiliary battery only.

Thoughts?

Lol no way. Always direct. Fuse the + line at the battery, no problems. You're just adding complexity (and a ton of failure points) for no benefit. That getup just sounds like a recipe for blowing fuses and other
crap. Radios have no business hanging off of internal vehicle bus wiring, in any shape or form. That's how you become "that guy" transmitting the funny noise on the repeater, or wondering why your car is doing weird things because RF is getting pumped into the car's internal busses, etc. (yes there's ways to fix all that crap, but it's not even worth going down that road). If you're concerned about emergencies get one of those LION car starter things and throw it in the trunk and top it off once in awhile.

The only way I'd ever add a 2nd battery to a vehicle is if it was something you were kitting out for operations where you sit in one place with the motor off for a long time, etc. Even then that sucks, because your gear isn't
getting the sweet nectar of 13+ vdc. (I have ocd, so I rarely if ever run anything only off the battery, except at stupid low power outputs for short period of time).

The only other time I'd consider it is if you had a jeep or a pickup that had a plow or winch on it....

Years ago I had a 160W VHF amp, a 700W 10-12M amp, a Yaesu FT2500M, and a 706mkIIG in my car with a 120A alternator, and one 900 CCA battery. I never once killed the batt to the point where the car couldn't be started, but then again I pretty much never operated the amps with the motor off. I had two power buses I brought into that car. One was for the radios (30 A circuit breaker) and the other was for the amps (75A fuse). For a basic setup you'd need less than half this, I would bring in a pair of #8's gas and oil resistant THHNs under the dash somewhere, maybe to some kind of distribution box etc, throw a 30A fuse/CB in the positive side and be done with it.

-Mike
 
Years ago I had a 160W VHF amp, a 700W 10-12M amp, a Yaesu FT2500M, and a 706mkIIG in my car with a 120A alternator, and one 900 CCA battery. I never once killed the batt to the point where the car couldn't be started, but then again I pretty much never operated the amps with the motor off. I had two power buses I brought into that car. One was for the radios (30 A circuit breaker) and the other was for the amps (75A fuse). For a basic setup you'd need less than half this, I would bring in a pair of #8's gas and oil resistant THHNs under the dash somewhere, maybe to some kind of distribution box etc, throw a 30A fuse/CB in the positive side and be done with it.

-Mike
Maybe it's more hassle than it's worth. I'll just run the wires to the battery and not experiment. The Subie turns out to have convenient additional grommets in the firewall for accessories, something that was missing on the van (one giant grommet for everything and zero expansion room) so it won't be as bad.
 
Believe Subaru OEM is a mid-range Panasonic. Very average OEM battery.

Been using the same Optima Red Top since 2010. It weighs 32 lbs vs 45 for OEM. Looked up the Group 25 Yellow Top and it’s 38 lbs and 690 CCA. Big upgrade.

But the highest capacity AGM battery we’ve found is the Odyssey Extreme. It’s 850 CCA, 65Ah. Little hard to find, expensive and weighs more (50 lbs) but what is peace of mind worth?

ODYSSEY Battery - Extreme Series
 
Be careful ordering from Amazon: if you read reviews there have been warranty problems. You can buy directly from Odyssey for $9 more.

There are dealers in MA, but very few near Boston. ODYSSEY Battery - Dealer Search

The Sears Diehard Platinum used to be sourced from Odyssey, but no more. We plan on putting an Odyssey in our boat next season.
 
I went with a Bosch Platinum AGM from PepBoys. Couldn't beat the deal, though will get a bit less CCA and hours than from an Odyssey or Northstar.

I think ColdDayInHell put one of these in his jeep and he likes it.

-Mike
 
It's still not as good as a Northstar or Odyssey Xtreme. But it's $150 vs $270-300 and most of the way there. The forester won't give a shit about 790 vs 900 cranking amps when the stock battery is 390.
 
Everyone has been bitching about Optima red QC on various boards for awhile now, not sure what the truth/fiction ratio really is, though.

I did, fewer cold cranking amps, shorter reserve capacity and more expensive. They apparently also suck now, since moving production to Mexico.

Johnson Controls bought Optima from Gates in 2000. They started moving production to Mexico. They had some startup problems and that was the factual source of the quality complaints. These were DOA or short-term failures so many got replaced on warranty. The problems were fixed within a few years and by 2009 JC had moved all Optima production (and a lot of their other brands) to Mexico and shut down the California plant. So somewhere in the late 2000’s they were back up to snuff.

Originally bought one for the WRX due to the much lighter weight of 32 lbs vs. 45 6-7 years ago. It is still in use. That worked well so replaced the battery in our Outback with one as well. Pep Boys had a great deal on it. The WRX sits for long periods at our place in NH and I want the Outback to start no matter what.

Not sure what they told you but the Optima Red Top has far more CCA than the Bosch AGM: 720 vs 650. The Odyssey is the highest at 850 for that size (Outback Group 25, Impreza Group 35). My understanding was that Hams preferred the Yellow Top.

AGM is the way to go no matter what the manufacturer or brand. The Bosch AGM is made by Exide.
 
Last edited:
Also, don't shit your pants when replacing the battery on a modern CRV. Go for a short drive and the christmas tree will turn off. I put a Bosch Platinum on the wife's car too.

The group 35 Bosch Platinum has 650 CCA, 110 reserve minutes, 53 amp-hours. Group 35 red top is 720 CCA, 90 reserve minutes, 44 amp-hours. Yellow top Group 35 is 620 CCA, 98 reserve minutes, 48 amp-hours. The stock Subaru Panasonic battery is 390 CCA, I figured the extra 70 CCA wasn't worth it for the red top, but the extra amp hours are for ham.
 
We make a copy of the original receipt, cover it in plastic and tape it to the battery, and put the original in the glove box. Then mark the top with purchase date. Some manufacturers won’t honor the replacement warranty without the original receipt.
The group 35 Bosch Platinum has 650 CCA, 110 reserve minutes, 53 amp-hours. Group 35 red top is 720 CCA, 90 reserve minutes, 44 amp-hours. Yellow top Group 35 is 620 CCA, 98 reserve minutes, 48 amp-hours. The stock Subaru Panasonic battery is 390 CCA, I figured the extra 70 CCA wasn't worth it for the red top, but the extra amp hours are for ham.
Exide filed for bankruptcy in 2013 after many years of quality problems. Hopefully those problems are behind them. The reviews are very good (https://www.pepboys.com/bosch-platinum-series-agm-battery-group-size-35/product/838876) and 48 month free replacement is great.

Some Subaru OEM batteries are Johnson Controls and some Panasonic. They seem to be pretty average. We always replace them before their fourth winter. AGMs are lasting us 6-7 years and counting.
 
Last edited:
They had some deal last year where if you signed up with them and bought these little felt battery rings, you got a $50 discount on the Optima. So we paid $172. I think it was a way to get around Optima’s price fixing, I mean, their MAP....
 
I've run lots of dual battery setups, and in fact am running one now.
What you are thinking of doing should work fine. I wouldn't use a motorcycle battery, though. A gell cell or AGM non-starting battery would be much better. Something like this: https://amzn.to/2BwzLKl
 
Also, don't shit your pants when replacing the battery on a modern CRV. Go for a short drive and the christmas tree will turn off. I put a Bosch Platinum on the wife's car too.

(Q: Is that from the power-fail, or initial low voltage?)

I've run lots of dual battery setups, and in fact am running one now.
What you are thinking of doing should work fine. I wouldn't use a motorcycle battery, though. A gell cell or AGM non-starting battery would be much better.
Emphasis on the "non-starting" (deep-cycle).
(Ham use you want total Ah, not instantaneous CCA).
Boat owners call them "house" batteries.
 
Back
Top Bottom