Just to add to this both my wife and I have 2018 M8 Softail Deluxes and we also live in the SE of England.
This is going to go on a bit but is all relevant.
Now initially mine Deluxe did not every register completely green, i.e. fully charged on the Optimate and not just one Optimate, we have three, all the newer CanBus type, even after several days between use, always remaining in the minor charging cycle.

I do have the full set of manuals and was concerned enough to run a few checks such as voltage, charging and more importantly the current discharge test, (parasitic drain) with bike turned off and off the charger, it recorded a very low drain of around 0.02 milliamps.
So I saw no real problem as there were no starting issues and after a few more cycles of riding and charging it started to go green and concluded the battery was fine.
My wife’s Deluxe never had the issue.

At the end of May we did a tour of Spain and a couple of days the bike were parked up not used, with no charger and were fine.
This month we went to the H-D 115th event in Prague, had a long distance run there at speed so should have had no issue with low charge.
We did not use the bikes for three days, my wife’s Deluxe battery was discharged down to 5.4 volts, nothing, jump started and charging, we took it to the nearest open H-D dealer about sixty miles, they did not have the battery tester it was in Prague but put it on the DigiTech and showed it was charging and the battery volts good.
So we travelled to our overnight stop in Fulda and went to the H-D Dealer there whom stayed open for us and they checked the battery, although it appeared to be OK on the tests, they were not happy with the condition of it and showed us the battery which, as they said did not look like a four month old battery and appeared to have moisture on it near the top so replaced it and were going to put the old battery on the tester the next day, unfortunately we do not know the result of this test as we had to leave in the morning.



So I am not too comfortable about this and thought about to conducting a battery drain test on my wife’s bike and leaving the bike off charge for at least three days to see the result of that and in light of reading this post will do it now rather sooner than later. I have all the test equipment to monitor it and even have a battery conductance tester but have never found out what the H-D battery base settings should be to set up the tester, the H-D tester only gives a good, pass or replace result and the voltage not the measured conductance value.


So when looking into the operation of the bike control/alarm system and if working as described in the manual/handbook there is nothing the operator can really do to leave the bike discharging, basically if you leave the bike on and not running, it will shut down in 15 minutes, if you leave the lights or hazard warning lights on they will shut down after two hours etc, also on the Deluxe all lights are LED and have significant lower draw than incandescent lamps.
My leaning from what I have read here is that if H-D are aware there may be a problem and assuming it is not faulty batteries, my thought would be that the bike is activating itself and causing a discharge without any external influence. e.g. the fob being present or a switch being pressed. This would have to be for some significant time for a good, charged battery to drain down to such low voltage though!
I would think the way to prove this would be leave a recording device in circuit with the battery to log any drain or significant discharge and the time and period it happens, I do not have this type of equipment to do H-D s fault finding for them, but will get onto measuring the discharge on the battery and leave my wife’s Deluxe off the Optimate and report back.



Steve

 

It's not easy, you need to remove the right side cover, you can get on the negative (ground) terminal of the battery, then try to get on the positive terminal (live) on the starter/solenoid under the battery, not a lot of room!

 

Cynically (Conspiracy Theory here) I wonder if the Dealers have been made aware of the issue with the battery and discharging, as when I was last at the Dealership and they knew we were going to Prague they were keen to show me and offered a discount on the new HOG Booster Battery Pack, I, in hindsight foolishly declined saying why would I need that with two new bikes and have you seen where the battery is on the new Softail, how wrong was I?

 

Right first off the Deluxe was steady Green on the Optimate, so moved the 'old ' Softail out the way side panel off along with the seat.




You can now see see below where to access a Positive (on the starter) & Negative connection (Battery Post) for a jump start without any further removal of parts, you do not have to remove the seat!

 

With the negative battery cable removed and the circuit run through an ammeter I logged the reading whilst still on the Optimate.



I then turned off and disconnected the Optimate and let it settle of around ten minutes and took a further reading with the current draw similar to when I tested my Deluxe under 2 milliamps at 13.82 volts
The mini clamp meter is not so acurate but still showed around 2 milli amps



Then a few hours later... with the draw under 1.25 milliamps at that rate it should be no where near remotely discharging a battery in three days!



I shall keep monitoring it off charge for the next few days.

 

Well my bike seems to be behaving itself - after a week of siting idle in the garage, it's dropped only 0.07v (went from 12.7v to 12.63v after a week)

So I'm thinking that's normal

 

You can add another one in the South of England. I had the same thing happen with my 2018 Fat Bob. Parked up after a ride, then went to start the bike the next morning and the battery was dead. At first I thought I must have left it switched on, but the on/off switch was definitely in the off position.

I removed the battery as I couldn't get jump leads to the positive terminal or to the starter motor. Charged it overnight on the Optimate and it has been absolutely fine since then, The problem has not manifested itself again even if the bike is left off the tender for a week it fires right up.

So I have no idea what the problem is, but it seems it is something that happens once with a new battery on the bike - or has anyone here had this happen multiple times on the same battery?

And as for jump starting these bikes - no chance with conventional jump start clamps. My plan is to add a remote positive terminal to the battery at some point in the future so I can get jump clamps on to it.

 

Update

After five days off charge and the current draw and voltage being monitored with an ammeter in series between the negative terminal and cable, being by-passed when not checking the load to ensure no additional discharge was caused by the meter, nothing significant.




The current draw is well below the maximum specified in the manual, averaging at 1.29mA, the reading fluctuates quite a lot and that would be the mean average.




I checked the draw when the ignition was off when pressing the Trip button and then kill switch around 400 mA and drops back after a short while to the 1.29 mA.

With the alarm sounding and ignition off a draw of around 800 mA.

Ignition on, run operated and fuel pump priming 3.24 A, ready to start lights on 1.02A

 

I'd say your bike is fine and it's not contributing to battery issues. Everything looks normal to me. You've really tested everything you can with the bike in the off condition. Nice job. Are you still experiencing battery issues? How about when you ride the bike for 1-2 hours? Is battery voltage remaining around 12.7 volts? Would say that the charging system is working correctly too.

 

My Heritage Classic is still with the dealer. It has failed twice, once the battery discharged to 7V and then a new replacement battery discharged to 5V. It would appear that there is a bad batch of batteries. Have I been unlucky enough to get two bad batteries? I'll let you know what conclusions the dealer comes too.