not sure why one is new and the other isn't, or even if that's true. i got it used through a buddy at a ford dealership and his paperwork showed one recent new battery, but the other could be new(er) too.
the charging voltage sounds low, but it does seem to be charging. she drove it as little as she needed to today and it seemed to be okay, so hopefully we're okay -- at least until i get home and can take a look at it!
can someone direct me towards a description of how the dual battery system is set up? or are they just wired together???
If there is an issue with the not so new battery, it will show up most when the truck is not running. I'll explain as best as I can.
The batteries are in parallel ,with no switches whatsoever. The batteries always attempt to "level "with each other. There is always a trickle (microamps)
flowing between one battery to the other ,as no two batteries are identical,even when new.This is perfectly normal. As batteries age,they dont age equally ,because of differances in ambient temperature,differances in cable length,and slight differances in battery manufacture,or even differances in the electrolyte(acid). THIS is normal
and unnoticeable. Problems arise when the leveling current gets too great,usually because of a cell in one battery beginning to short.When this happens,a full cell short will cause one battery to become a theorectical 10 volt battery while the good one is a still a 12 volt battery. The shorting is caused by normal flakeing of the battery plates onto the bottom of the cell.
You can have a situation where a battery is approaching end of life. It will discharge during downtime but still seem to work fine...BUT the alternator is constantly having to recharge at 100 percent duty cycle over and over and over....combine that with some alternator rebuilders using
imported CRAP electrical components... beware of what to suspect if
your new alternator fails prematurely.
IF possible,until you return home, is it practicle to have someone connect a trickle charger to the truck between uses??? A simple cigarette lighter charger would be good.....or even a cheap solar charger would help.
When you get home.....determine first if your battery has removeable caps.. If so proceeed to Walmarts or an automotive store and buy a hydrometer.That will cost maybe a grand total of five bucks. Its a simple glass device with 5 floating balls designed to measure the specific gravity
of each cell's electrolyte.A perfectly good cell will float all 5 balls.(when charged) Usually , as a battery starts to fade,the POST cells will show a change first and still has life left in it. In a single battery setup this is no cause for alarm. In a dual battery ,parallel setup,this is a cause for alarm, if both batteries are not similar . In fact the battery with the end cells showing 4 balls floating could probably be successfully used in another vehicle for a couple years BUT not a dual battery setup.
If you batteries pass the hydrometer test ,the batteries are probably ok for now and you wont need to have lifted them out of the truck.Its a reliable means of checking on the health of your batteries.(been using this method for 41 years.)
If one of the cells is low on acid...myself I use battery acid.If i am out on the highway...I will and have used TAP water...(It will last long enough for me to get home.... The battery is probably doomed to die anyhow)
The hydrometer measurement will NOT help you to isolate batteries with high plate resistance.....but the symptoms you describe are not a high resistance fault. A LOAD test is needed for that issue. That condition is usually probable when the charging system appears to be charging (13.6-14.3) ,all the connections are good,but the battery just isnt "putting out" High plate resistance usually occurs after a battery has sat DEAD for weeks.(A battery sitting dead builds a sulfide coating on the plates ...as on someones weekend boat or jetski.
Battery replacement on Superduties should be done similar to tires.Always try to have a matched set......unless you want the headache of keeping track of them. can you imagine the headache of 4 trips to a tire dealer to replace a set of tires..one by one???
A dealer should know better than to replace just one...but it happens ($$$$)