M696 - battery charging

[alibaba]

 
M696 with fairly new stock battery (this battery has never become discharged requiring charging) -  this bike is ALWAYS on a battery tender when not ridden.  I am looking for some assurance that I do not have a potential problem here - at the end of a ride the battery voltage reads 12.3 to 12.5 at best.  After the ride, when I hook up my Battery Tender Jr.  it is red.  Overnite it changes to green.  But when I check the battery it is as low as 12.1 to 12.3 volts.

Stator check - at idle it is 13.1 to 13.3 volts at the battery and from 3000 RPM to 8000 RPM it goes from 13.6 up to 13.8 volts . 
I believe from earlier posts that this is a correct working range.

Question - since the battery tender and the stator seem to be working is it normal for the battey to only show a charge of 12.1 to 12.3 volts after sitting overnight on the charger.  I can never get a real healthy charge on this battery by either the stator or the battery tender.

Maybe
Thanks,
Ron

[Howie]

A conventional (wet) battery will read 12.6 = 12.8 volts when fully charged.  AGM batteries (like in your bike) will read higher even though, if you search the board, I do use the 12.6 to 12.8 figure.  Some, probably most "battery tenders" will not fully charge an AGM battery.  Your bike charging system certainly should though and yours seems to be operating correctly according to your post.  Before condemning the battery check the positive cable connection at the battery for high resistance, but you probably need a battery.

[alibaba]

LOL  - Yes - I am over diagnosing a working condition to:

#1 learn something

#2 anticipate a problem before it starts

If I worry enough about it, it will probably occur.   ;-(

[H-2 CHARLIE]

   Maybe  its not holding a charge ?    Have a load test on the battery .                                                                                                         

[Duc796canada]

I'm having the same issue on my 796 now. It started as a no start, I checked the voltage it was 12.3V, I put it on a charger and it shows green, but it won't start the bike. I guess I need anew battery, the bike is barely a year old and being said it is ridden barely 6 months out the year. I'm looking into a Shorai now, good excuse to get one

[R0CKETMAN]

I'd say normal and perfectly acceptable. The green being the maintenance mode, it may be that the tender prefers to keep it in that range....reminds me I need to put a BT pigtail on my 1100 soon.

[D-Mac]

Not sure if this will help, but BMW uses the same type of battery and a lot of guys on those forums complain about this exact problem (battery kept on a tender, light is green, bike fails to start).

Two possibilities I've heard about:

(1) Most 12v battery tenders are 0.75amps. Apparently, this type of trickle charger will hold batteries at a lower state of charge than the larger 1.25amp trickle chargers (e.g., Battery Tender Plus), which over time causes the battery to wear out much sooner than it should. I bought a 1.25amp charger for my R1200RT last fall and sure enough - when the "standard" 0.75a tender would show green, the "Plus" version would continue to charge for over an hour before the light on the box went green (the packaging for this product has "use with AGM batteries" written right on the front as well). My local dealership claims that dead batteries happen a lot due to this difference, and of course he recommended a special "BMW" version of the charger. Looking at it, it's just a relabeled Battery Tender Plus, so that's what I use.

(2) These types of batteries are prone to sudden failure. Voltage can read normally, but the battery is toast. Unrelated to issue #1. I'm going on memory, but I recall that it has something to do with the physical construction of the battery (some kind of internal short).

[Howie]

D-Mac is correct, some battery chargers may not be capable of fully charging an AGM battery since they require a higher charging rate.

[Duc796canada]

Ctek is one of the chargers a lot of people are using and same one I have. it should be fine, yes?

[Howie]

Ctek is one of the chargers a lot of people are using and same one I have. it should be fine, yes?

No idea about your charger, but it is easy enough to find out.  Most "tender" type chargers and "smart chargers will go into "float" (maintenance) mode when they reach about 80% of full charge, greatly reducing charging rate to avoid battery damage.  Usually charging voltage is reduced to 12.8-13.2 volts, fine for a conventional battery that is fully charged at 12.6-12.8 volts, but not enough to bring that AGM battery that has higher open cell volttage when fully charged up to 100%.

Back to your charger.  Charge the battery with a voltmeter across the terminals.  When the charger goes to "float" does it read 13.5 volts or higher?  If not, would I panic and go buy a new charger?  Not me.  80% or more should start your bike.