Scotiapilot

SO my SUb has a dual battery set up and last September my car wouldn't start and I replaced one of them. The other is from 2011 and show to be bad when tested.


I have no idea how these systems work, but last sept the new battery let me start again and well..............I forgot to replace the second battery


The past few days I would get the starter to click but no work then it would suddenly it would start.


it was getting worse.


This morning same thing so I took I to autozone they replaced battery and still it wouldn't start.


It took a jump start from another vehicle for it to start. new battery seems fully charged now.




Question. How does this dual battery system work........I wonder if the bad old battery ihavent replaced is affecting the new battery.






Any help would be appreciated.




Yes tomorrow I plan on replacing the 2nd battery. I just want to make sure my starter isn't going out

73shark

Not sure how your 2nd battery is set up but it sounds like your starter may be going Tango Uniform.

Scotiapilot

Plot thickens, after studying dual battery systems I have learned that my setup is a dual battery NON isolated system. This means that my battery starting system uses both batteries all the time. If one is bad (depending on why it is bad) it can pull down the new battery.


It would appear that my 2nd battery may have a shorted cell and is not allowing the new battery to stay charged. It is actually discharging my new battery while the system (for lack of a better word) is equalizing. This is why I can jump start it. Run it, let it charge on the alternator then after it sits it will take down the new battery to the point of discharge and not allowing it to crank.


SO if you are getting a dual battery system make sure it has an isolator. This will keep the starting battery alive at all times and only allows the 2nd battery to charge after its started.


My 2nd battery is from 2011 and it does test bad. it has 12.4 volts but when the ignition is turned on it drops to 8 volts.


When a cell shorts out it means that the cell is actually discharging or grounding out the positive charge thus it is taking out the other batter that is in parallel




73shark. Thank you for your input.

73shark

I am not sure how your factory dual battery system is connected but the ones on this forum that I remember were isolated so the starting battery could not drag down the auxillary battery. IIRC, they were using the aux battery for accessory power in order to prevent running down the starting battery.

Scotiapilot

Yeah it can be that way, It appears it would be a simple change. Ill consider it next. It appears this system was installed when it was new. So in 2008.

intheburbs

Building a factory TP2 isn't cheap, but it does eliminate issues like this. I've done it in both my trucks. No issues whatsoever.

Typerod

My dual batt setup, does not have an isolator. But when I first installed the setup, I bought two brand new Optima Yellowtops that were born in the same month and year. From what I have learned from research, that is the best way to have a dual batt setup that is not isolated, is to start with two new, fresh batteries, that are good.

I've had this setup up for 5 years now, and no issues. It just sucks to drop quite a bit of money on two new batts everytime one may need to be replaced. I would like to have an isolator installed but I'm worried I won't be able to do a nice clean install.

Scotiapilot

yup you need two fresh bats for sure. unfortunately I didn't have the money to replace the 2nd battery last year. I totally forgot about it.


Lesson learned

SWHouston

Some very good info/experiences related here...

Just for clarification...
When you have two batteries, connected where they start/work/charge/discharge together, the second battery is called "Supplemental". 99% of the time, when there is a problem with that system, it exists in/with both batteries. Therefore it is recommended that they always be replaced in like pairs. Customarily, a Supplemental Battery is most regularly necessary when there is a condition of hard stating or very cold starting conditions. It is not recommended that this system be used for extended periods of use of accessories without being recharged, just because there are two batteries available.

A system where you have two batteries, where only one starts and operates your normal functions, and the other is reserved for when your engine is not running, and separated from that start/run system by a special relay/isolator, is called an "Auxiliary" system. Given the dual function, problems can occur in one battery and not the other, so, a single battery replacement can occur, and they do not need to have a compatible amp rating, size or age with the other (sup/aux) battery.

The Auxiliary system, can be set up with any number of functions, which control Radios, lights or other electrical equipment, and is very advantageous if you are Towing a trailer which you may be in for some period. Or, intend to use the electrical components of the host vehicle for periods of time without starting it for a recharge.

Using a "Deep Cycle" battery in an Auxiliary system is highly recommended...
Standard "start" batteries do not do well when they are discharged well below 12.4 vdc, or for extended periods of time. A condition called "Calcification" occurs, and is almost a guarantee for battery failure, unless it is halted/recovered correctly. Some Battery Maintainers have the Recovery feature.

Any Auxiliary or Starting system, which is not used/charged regularly, is prone to Calcification unless proper voltage maintenance is available during the nonuse periods. By the same token, an Auxiliary Battery which is connected to a regularly functioning system for extended periods and not used (remains fully charged) is prone to have shortened periods of functionality. ie: "use it or loose it".

Scotiapilot

Both batteries replaced tonight, starter really kicks off, lights are brighter while not running the engine,


Curiously the engine runs MUCH smoother, idle is seamless.