Are We Over Charging Our Batteries???...
I believe by installing a high output system on a bike that does not have the demand, you are actually over charging the battery shortening the life of the battery.. The following excerpts are out of my 98 Softail FSM and my 2013 Dyna FSM.. Take a look at the difference in standing voltage readings that determine the state of the battery.. Why the difference?? Has the MOCO determined that bigger/more is not better?? Or is it because the type of battery?? One being a sealed lead/calcium sulfuric acid and the other a sealed AGM lead/calcium sulfuric acid, hmmmm, or is there a difference and if not why the different ratings?? Regardless of the 2 different designs the recommended charging method has changed.. Why??
Look at it this way, if a standing voltage reading of 13.0 v according to the chart the MOCO states (for the 98 FSM) or 12.7 v (for the 2013 FSM) the battery is at 100% charge why do most systems charge at a rate of 14.3-14.6 v.. Are we over charging at this point if the the load on the battery is not there and are actually shortening the life of the battery? In the 2013 FSM the MOCO states "The use of constant current chargers (including trickle chargers) to charge sealed AGM batteries is not recommended.. But isn't that what the bikes charging system is?? A constant current charger?? And if so are we actually over charging the battery and shortening it's life?? Hmmmmmm...... Food for thought..
This is why I went to a lower volt charge rate system on my Evo.. It's a Cycle Electric low volt system of 13.5 v.. Time will tell if this is the answer or not.. Back when the 98 was new, I believe they didn't have AGM batteries but now most all lead/calcium batteries are changing the recommended charging requirements.
If this don't make sense I understand but I hope it does to and maybe get more input on the idea/concept of why batteries are failing sooner than they used to..
Last edited by 98hotrodfatboy; Mar 6, 2026 at 09:18 AM.
The voltage regulator maintains the voltage at a constant level; excess current is dumped to ground.
Last edited by Dan89FLSTC; Mar 6, 2026 at 03:34 PM.
full blast
do not think so
first off you are looking at an average chart of charge vs capacity. all batteries are not the same even in the same class. actually that charge voltage could go to 16 on the short term side with no ill effects.
look at it this way. if you push bb's into a straw from both ends, eventually the straw becomes full so in order to move more bb's, something has to give. if you have 12.7 on both sides, then there is no current flow hence the regulator's job is to force more current across the load that means there has to be an excess. why? batteries are resistive loads and that varies on condition of the plates, electrolyte among other things. batteries are also like a capacitor and absorb ac hash in the system and trust me electronics do not like ac ripple. now factor this in, look at the system, the machine actually runs off the regulator and the battery making up any short fall, hence a good system needs 20% fudge factor to make sure the battery can charge.
hd uses a couple of diff regulators and none of them dump excess current to ground even the old mechanical ones did not since current can not flow across an open contact nor an electronic semi-conductor unless it is gated on.
by far and large, the system keeps the regulator in check and nothing is dumped. however, if you run outside the intended parameters, aka, high rpm, the system starts to saturate this is where the protection circuit comes in, it will bleed the "ac" component to ground while the charge side of the regulator does its thing, charge the battery. the "ac" component is a fraction of the "dc" component. all of this is controlled by zener diodes that trigger semi-conductors so the excess is bled off and that is on a need be basis.
there are regulators out there that are self contained for lack of a better word sorta like a scr system where output is timed to points on the ac wave form like time on/ time off. in between these points nothing flows. like a fuel injector duty cycle.
Last edited by bustert; Mar 6, 2026 at 04:10 PM.
full blast
do not think so
first off you are looking at an average chart of charge vs capacity. all batteries are not the same even in the same class. actually that charge voltage could go to 16 on the short term side with no ill effects.
look at it this way. if you push bb's into a straw from both ends, eventually the straw becomes full so in order to move more bb's, something has to give. if you have 12.7 on both sides, then there is no current flow hence the regulator's job is to force more current across the load that means there has to be an excess. why? batteries are resistive loads and that varies on condition of the plates, electrolyte among other things. batteries are also like a capacitor and absorb ac hash in the system and trust me electronics do not like ac ripple. now factor this in, look at the system, the machine actually runs off the regulator and the battery making up any short fall, hence a good system needs 20% fudge factor to make sure the battery can charge.
hd uses a couple of diff regulators and none of them dump excess current to ground even the old mechanical ones did not since current can not flow across an open contact nor an electronic semi-conductor unless it is gated on.
by far and large, the system keeps the regulator in check and nothing is dumped. however, if you run outside the intended parameters, aka, high rpm, the system starts to saturate this is where the protection circuit comes in, it will bleed the "ac" component to ground while the charge side of the regulator does its thing, charge the battery. the "ac" component is a fraction of the "dc" component. all of this is controlled by zener diodes that trigger semi-conductors so the excess is bled off and that is on a need be basis.
there are regulators out there that are self contained for lack of a better word sorta like a scr system where output is timed to points on the ac wave form like time on/ time off. in between these points nothing flows. like a fuel injector duty cycle.
The regulator limits the DC output to the battery voltage and sheds the rest to heat.
AI explains it better.
In a Permanent Magnet Alternator (PMA) with a wound stator, the voltage regulator works by monitoring the output voltage and shunting excess alternating current (AC) to ground, converting it into heat, rather than controlling field strength.
Because permanent magnets cannot be turned off, the regulator uses diodes or thyristors to short stator windings when voltage exceeds the limit, acting as a shunt regulator.
Now it is true Harley owners use even quality maintenance chargers too much. And it's not that they hurt the AGM battery.
What it does is they are not qued in on a battery wearing out with the typical hesitations and yes kick backs from a battery low on cranking amps that bang the starter.
And a guaranteed the last start you get is one morning when you leave home.
PS Dan taught me the above and he's rarely wrong on here.
Your welcome..
And thanks Dan.
Last edited by Jackie Paper; Mar 6, 2026 at 05:20 PM.
I am certain a large percentage of the lead used now would have been recycled.
Another generalization I find is that a regularly used bike, or one that uses a trickle charger will have a longer battery life.
The resting voltage (SOC state of charge) doesn't really relate to the charging voltage .
The charging voltage is always higher than the fully charged resting voltage.
Under-charging can also cause sulfation, and reduce capacity over time.
There is a whole science related to battery charging and longevity, but not so easy to maintain ideal charge in a HD.
A colder battery needs a higher charge voltage than a hot battery, but most simple charging systems don't compensate for that.
Also running at lower revs with headlights and accessories, the system can struggle to maintain charge.
System designers pick a middle ground that works in most situations.
I have worked with large capacity UPS systems, and the battery life is around 10 years for quality batteries.
The float charge voltage is normally 13.8v, with a boost in voltage after any discharge of close to 14.7 .
Sorry for rambling on !
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I've always wondered if we overcharge our batteries by keeping them on tenders 24/7 while not riding them. The new charger/maintainers do a better job of keeping an optimum charge in the battery, but those constant amperage (even lower ones) can be hard on a battery if there's more amps constantly going in than the bike is "consuming" by just sitting there, no?
I've had systems consistently show 14.4v when running (depending on how accurate the gauge was), and the battery lasted for many years. But it was a daily driver too.
The best way to keep that battery charged is to RIDE IT! But I understand that isn't always possible.
Always looking to learn, and this is simply IMHO.















