This is probably a stupid question but....
Does it matter which Battery i hook this too

Dont remember which 1 exactly but it seems as if u un-hook the left battery everything in the truck resets but u can un-hook the right w/out memory failure's.
Ive had to remove batteries to gain access before & cant remember which did what exactly but iam guessing even though they are hooked in series it still would not matter which one i put the charger on, should charge both equally...Right

Just ordered a brand new Battery Tender Jr on eBay for $24

 

Tge one on the passenger side runs under hood componets. Driverside is in cab.

 

The two batteries are hooked in parallel, so it doesn't matter which one the tender is on. If you want the plug-in closer to your block heater plug, then put it on the passenger side.

 

I put mine on the passenger side because the battery was slightly closer to the front of the truck and the leads were barely long enough to stick out from under the hood. I couldn't do that on the driver's side.

 

My dad keeps the small battery tender on his truck all of the time..he drives it about once a month..his last batteries lasted 12 years.

 

Thanks for the Info guys

 

My truck sits during the week I try to drive it every weekend. The batteries seem fine but when it's cold the FICM fluctuates down to 43-44 so
I installed one of these on mine on the drivers side battery. Ran the cord down right behind bumper. Works great!

 

Double post sorry

 

in 35 years of being an electrician, and working on numerous
battery systems, i have found this battery charger / desuphator
to be second to none:

Batteryminders Specials | BatteryMinders.com

BatteryMINDer Model 12248: 12 Volt 8 Amp (12V 8A) Charger/Maintainer/Desulfator

all battery chargers are NOT created equal. most of them will cook
the battery if left on.

the quality of the charge cycle of this unit is as good as computer
room battery backup differential float chargers costing several
thousand dollars. i've put it up on an O scope and "scoped it out".

seriously. i have three of them personally. one is mounted near
my main fuse block under the hood, and the plug goes down next
to the block heater... if i have to plug in the block heater, the
charger gets plugged in, as well.

it's an 8 amp output, but it will, by virtue of it's charge cycle, charge
up two flat oddesy group 65 batteries to full float charge in about
8 hours or so. once it gets them to full charge, it begins to desulphate
them, and can be left on indefinitely. longer is better. it took about
two weeks, but i completely reversed two batteries that were so
sulphated that they wouldn't charge. they have more CCA available
than two brand new batteries of the same mfg. and type, i've load
tested them against two brand new ones. they are six years old at
this point.

where you hook it into the system doesn't matter, as long as it
is a good connection. i have mine attached to the primary
cable on the main fuse block on my van.

the unit is not "waterproof", but it's very water resistant.

 

FICM volts are way too low, better send it off to ED asap for a rebuild.