With our battery setups can we run a maintainer on each battery or is two overkill? I have two of these for reference:

 

You should be fine with one for both batteries. Its what I do.

 

One battery maintainer is fine.

If you can,( like if the cables will reach) put the positive battery charger alligator clip on one battery and the negative battery charger alligator clip on the other battery. This makes it so both batteries are charged to the same voltage at the same time.

If the cables won’t reach to allow for one clip on each battery it’s not the end of the world or anything, it’s just the one battery that the charger isn’t connected to will have a very slightly lower charge voltage due to the resistance of the cabling connecting the two batteries. Which will ever so slightly reduce its service life compared to charging both the same.
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I haven't found that to be true.

 

I have one already hardwired to the drivers side battery, but It doesn't work when it's COLD out and I noticed my voltage was into the mid 11's so I quickly put my second charger on the passenger side for 24 hours then ran the truck on high idle for 30 minutes and now the passenger side maintainer is keeping the voltage at 12.5 and I'm just wondering if both chargers were to be running at the same time would that do any harm?

ALSO can a hardwired charger/maintainer that's not working properly drain a battery?

 

It can drain it if the diode is hurt. I would pull it off and try using only the 'good' one. The one I have right now on my truck is one of my 'old school' tenders. You don't need much to keep them charged well. The newer ones are possibly better, but these have done well for me. I'm only trying to show it doesn't have to be a high amp.

 

How cold does it get in your neck of the woods?

 

I would add you should keep an eye on the "brick" chargers when they get to the maintenance step.
The first 3 or 4 charges with mine did a good job keeping my battery maintained. The solid green light came on after full charge to indicate maintenance mode.
About 6 months or so after buying the brick charger I noticed it no longer entering maintenance mode and in a couple more months it would get up to a pulsing green light and after about 10 or 15 minutes the red light adjacent to green would come back on then the second and third red lights would come back on so that all reds and the green were on at the same time.
This battery quit on me after purchasing it only about 3 or 4 months before so I got a brand new replacement and the brick charger was doing the same thing to it.
I had bought the brick charger off of the well known internet store so emailed the mfgr. I also had gone to mfgr.s web site and completed registering the brick and hoped to get my money back on this defective charger. No such luck. Several back and forth emails wound up them just quoting out of the "Owner Manual" what the brick is supposed to do, never addressing my problem. They've sold tens of thousands of these things so why bother with one customer. Some reviewers on the "Ama...." site had complained about the brick killing their batteries as well.
Just don't trust the brick charger. It may work for 20 years like the first Tender Plus I had or it may crap out in a few months. If it begins to have difficulty reaching maintenance mode keep an eye on it. It did the same thing to both our car batteries which one was new at the time.
The charger evidently loses its brain when going into maintenance mode now and actually goes backward and thinks the battery is quickly draining and it tries to keep up.
Cost me a new $280 battery. $100 for the brick down the drain.... I went back to the old Battery Tender Plus by Deltran. They always work.

 

One thing I will add, is some of the small chargers are not battery specific (wet cell, AGM, Gel etc). I used a small unit for years prior to what I have now, but some higher end batteries are finicky.

The NOCO is what i have in a single bank hooked to the right side battery. Eventually I will upgrade to AGM and this charger differentiates battery styles.

If your current is not working in weather get rid of it and buy a NOCO (single or dual)....you will never be dissatisfied.

 

I really like my NOCO 10! Does well w/ my AGM batteries.

 

>>How cold does it get in your neck of the woods?

Nothing like the Great White North. I do it for battery maintenance, as my truck can sit for weeks. Due to the pavement, Newark Airport is a few degrees warmer than we are.

 

Due to the truck camper I've not used the truck much this winter and I'm on the same tank of diesel since September lol so keeping my newer batteries charged up is priority #1 for me.

 

LOL, I hear ya. Not quite as bad as you, but I hadn't filled up since November.

 

I'm still over 3/4 of a tank and once it warms up I'm going to unload the camper and get to refurbishing the water damaged walls/roof. Should be fun lol.

 

As stated in another post, these types of charges can fail and appear to be charging but are not. The circuitry in the chargers is complicated and has many points of failure compared to the old transformer-type chargers. My NOCO charger failed. I'm now using a CETEK. Pay attention to the charging lights and double check voltage when they are not operating normally.