So I actually made this observation on my boat with the 5.0L exploder motor I built... Figured this was the most appropriate place for this post since the motor is the only thing Ford involved...
Ever since completing the rebuild on the motor, I have been having issues with getting the batteries to hold a charge; there had also been issues with burning up starter motors which were resolved by buying the most heavy duty replacement parts I could find. In hindsight this was probably overkill but hopefully things are now going to be much more reliable.
I had troubleshooted everything from the ignition switch to the starter solenoid and of course the starter. I had questioned whether I crossed wires somewhere or if perhaps something had been left unhooked. The engine ran fine with the batteries disconnected so the alternator must be good (I never ran it for very long like this as I only wanted to see if there was adequate power to keep things running). But whenever I went to start, it always needed a jump. This is with two batteries; since two batteries seemed to struggle with turning the engine (bolted to an outboard so a bit more to turn than just a motor) over I never thought to try just one...
Since they are both walmart deep cycle marine batteries, I figured I would take full advantage of walmarts willingness to test and charge. The last time I did this was about a year ago; both tested good at the time. They have largely sat since then aside from a couple of starts each month when I was troubleshooting or testing; usually these starts required a jump. Low an behold, walmart finds that the newer of the two batteries (dated 2012) has a bad cell. The dude says the older battery (dated 2011) is probably on its last leg as it was really low on juice. I left the store committed to never buying another walmart battery (I didn't actually purchase these two as they came with the boat). These things had barely been used; admittedly this could have contributed to the early demise.
Having nothing to lose, I decided to inconvenience a friend and had him hook the older battery to his 'smart' charger to see what happens. A week off the charger and it still had something like 95% of its charge. It must be good so I install it back into the boat.
Since I purchased the boat with a seized engine, I didn't know what a good healthy crank sounded like; I assumed I did when it was being jumped but I didn't. This thing cranked really quickly and seemingly effortlessly; just by the sound I knew it was better. It fired right up and ran smoother; it was sounding a bit loppy at idle. Before this, when it would run for 5 - 10 minutes, parked right out side of my garage, the fumes from the exhaust would make your eyes burn. I thought this was normal as its got a 2bbl Holley carb. I could still easily tell it was carburated exhaust but it was at a tolerable level; I even asked my wife if she noticed a difference and she agreed it smelled way better. Other issues that seem to be resolved include the solenoid staying partially engaged when the key is released from start to the on position. My guess is this phenomena is also related to the fried starter motors.
I always assumed, based on my own personal experiences and from what others have told me, that a bad battery can have some really weird symptoms, that this was really truer for newer vehicles; the older cars it seemed, were so much simpler that a dead battery would act like just that. Never in a million years would I have thought that a bad battery could affect the emissions of a carburated engine but in hindsight, it really isn't that far of a stretch since a short in a battery can cause a system drain that leaves less juice for the ignition system.
I very much appreciate the old adage of learning something new every day... Just thought I would share! Now to see how long this other battery holds out...
I would say the battery that had a dead cell was causing the weird running problems. Note that something like that can actually kill your alternator.
Even deep cycle marine batteries will die slowly if left alone for long periods of time. If you were only starting the engine once a month, you should put a trickle charger on the battery to keep it topped off. Otherwise, your new battery will again die after a few months of no use.
BTW, I recently had to replace a Walmart battery, but I had been using it for over 7 years. The symptom I noticed leading up to its final death was that the radio would lose its settings every time I started the engine. I was more used to the slow starter crank from a weak battery, but did not see it this time, until the last morning when I turned the key and the starter relay just buzzed.
The battery is the heart of the entire ignition system. It's only purpose is to start the engine, basically. Neglecting it leads to expensive component failures that are completely unnecessary! One thing that a lot of people forget, if they go flat (need a jumpstart) it should ALWAYS be put on an outboard charger as soon as possible and fully charged. Deep discharges should be avoided as the capacity will never be the same and possible cell reversal.
Dual batteries connected in parallel are always charged in parallel, and most retail chargers aren't "sized" properly for this. A small tender or smart charger works great for maintaining an already full charge but they will typically time out (or should) on a weak battery to avoid boiling out the electrolyte. A "slow" charge for example on a large dual battery setup might be around 20 amps.
What really clicked for me was A. Determine exactly what kind of battery construction - Conventional, "Maintenance Free" AGM? The charge is different for each. B. Determine the charge profile of the battery at a site like http://www.batteryfaq.org C. Hang a voltmeter on the battery while charging and observe the voltage applied and see how it aligns with the chart.
Notice that it is temperature dependent, and a battery only _approaches_ a full charge when it reaches approx 2 volts above the nominal resting voltage of say, 12.8 volts. Most peoples eyes bug out when they see 16 volts applied at the end of the cycle but that is what is necessary to equalize cells in a modern battery. Batteries "like" to spend time at or above a full charge for several hours, especially since they spend so much time in a state of discharge.
It is possible to overcharge a battery but it takes dedication. It's better to use an inexpensive battery with a quality charger than neglect a top of the line 1000 CCA monster. Once you get the gist of things, your batteries will last a LOT longer and give good service for your money.