• Welcome to the forum website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Online Forum Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this forum website.

    If you have previously registered to use this forum website, you should log in now. CLICK HERE.

    If you have never registered to use this forum website before, please CLICK HERE.

Battery weak after ride - C Rapide


Well Known and Active Forum Website User
VOC Member
I have a 2 maybe 3 year old YTX14-BS 12v 12Ah battery fitted to my C Rapide and recently the battery seems rather flat
after riding a while. Has difficulty starting once engine is stopped.
Voltage was 12.17v when I checked it today after a ride and it did cut out just as I was turning imto the drive.
Headlight looked pretty dim aswell.

The Millers ammeter is on '0' when doing around 60mph. I think the charging system's ok as the needle
rises when engine is revved. Headlight also brightens.
Charging with the optimate results in the usual green lights and doesn't seem to drop any voltage.

There is an electric start fiited to the bike but don't use it that much as I think it needs a 14Ah battery. I can only find the
YTX14-BS in 12Ah rating.
Maybe the battery's up for renewal.
Any help appreciated.


Well Known and Active Forum Website User
VOC Member

I am not an electrics guy, but three years old can be very old on a small battery that is not used everyday. Also, 12.17 seems too low. I would think well above 13 is the lowest it should be after a ride. I would not start a race on a total loss ignition that measured 12.17.

Is your bank account good enough for a Shorai, which seem so popular?



Well Known and Active Forum Website User
VOC Member
I would do lots of research before buying a LiFePo4 battery such as a Shorai or Ballistic. I have owned two and have gone back to conventional lead acid.
The Li batteries are not designed to work with our antiquated charging systems, or even an upgraded system such as a Alton.
With the Ballistic, the warranty is void if the voltage has ever been pulled below 13 volts. When pulled below this voltage an electronic telltale is left behind.

My $170 Ballistic lasted just 18 months. It is still under partial warranty, but there is no point on acting on it as I know the system has seen less than 13 volts, in fact the resting voltage on that system is generally around 12.8, or lower after a night run.

It was suggested to me that a third Li Battery brand called Deltran might be better suited to the job.. I contacted the Deltran and learned that my problems with the Ballistic batteries are to be expected in this type of electrical system. Li batteries work best in modern hi output systems that run to 14.5 volts and produce a positive charge even with lights on at idle. I asked if Deltran LiFePo4 batteries (same type as Ballistic and Shorai) would live OK at 12.5 to 13 volts, which is where most of these old systems tend to run. Here is the answer: Hello Glen,

Unfortunately the answer to your question is no. Nobody’s 12.8V LiFePO4 battery will work in that situation. These batteries need to see at least 13.6V to maintain a full charge. Anything below that will not ever charge the battery to 100%. You end up with much less capacity that you need. The state of charge of a LiFePO4 battery sitting at 13V is only 30%. At 12.75V it is only 10% charged.

Lead acid batteries are your best bet because your system’s voltage is just enough to keep them fairly charged.

Best regards,
Last edited:


Well Known and Active Forum Website User
VOC Member
Hi Glenliman. You do not tell us what charging system you are using but the battery volts are certainly too low after a run. It should be well over 13 for an hour or two after a decent run. With a decent modern charging system you should not be writing batteries off after a few months. Even cheap lead acid batteries last years with a 'Walkernator' set up and I would expect the same from any modern charging system. If you ride with the headlamp on for a while does the amneter still register zero charge or is there a continuous charge of a few amps as the system tries to bring the battery up to 13.4 volts? Do you ever see a discharge reading on the amneter with the lights on and the engine running at over a thousand rpm? If so then, in my opinion, the charging system is not up to the job.


Well Known and Active Forum Website User
VOC Member
I 've got an Alton, it appears to be working just fine. I have used lead acid batteries with it in the past, no problem there, even the cheapies last four of five years.
The problem isn't the charging system, it is that Lithium Ion batteries are not compatable with our systems, the "Walkernator" may be an exception.
The first problem with Li batteries is their rating system, Pb/eq, or lead acid equivalent. The sales departments quote these numbers as though they are comparable to AH ratings in lead acid batteries. They aren't even close. To get an approximate AH rating from a LI battey's Pb/eq rating, divide by 3. So that is the first problem, a Li battery with a Pb/eq rating of 9 was sold to me to replace a lead acid 9ah. The actual storage capacity of the 9pb/eq Li battery is 3ah, much too small for the job. Couple this with the fact that the 3 ah is only available in a system that is maintained at about 14 volts, and you have a real problem. At 13 volts you only have 1 ah of power remaining. This means that the battery will go dead very quickly when idling in traffic with the headlight on (discharge).
Once the voltage in the Li battery drops below 12.5, the battery goes into limp mode to protect itself , so voltage drop off a cliff. When discharging, voltage goes directly from 12.5 volts to around 5 volts. If you have point coil or EI ignition this means that the engine will die and you are up a creek. This is just how these batteries work , and it took me awhile to realize it.
I have talked with people who have used them with older systems and had a satisfactory result. Generally these are bikes that do not rely on the battery for ignition. If that is the case, you can get by with nearly anything.

Last edited:


Well Known and Active Forum Website User
VOC Member
Thanks for the replies.
I always use the headlight for daytime riding and I've only been checking the charge the since the flat battery problem.
Seems to stay around the zero mark when cruising.
The bike has a Lucas Rita ignition system fitted by Conway Motors.

I have Oddysey PC680 drycell batteries fitted to my BMW R60/6 and R1100RS. I used to use lead acid batteries on the R60 and have been left stranded a couple of times due to flat battery.
The Oddysey batteries are a must for BM's and are literally fit & forget.
Need something like this for the Vincent but needs to be YTX14-BS size due to the battery holder.
Is there anything available like this in the UK?


Well Known and Active Forum Website User
VOC Member
I use a Kaw KZ650 battery in my Rap. I needed to space the bottom claw for the hold down rod.

Regarding batteries in BMW's, I put an undersized battery in my '77 R100/7 and it has done just fine.

Comet Rider

Well Known and Active Forum Website User
VOC Member
Hi Danno,
Have a look at MOTOBATT batteries.
They are similar in construction to the Oddesey range, but unlike the original 14Ah battery you are running, will be a slightly higher Ah rating for the same size.
They also have the advantage of having 2 sets of output terminals, aso it does not matter which way round you fot them. ;-)

I recently fitted one to my BMW and it was far better than the original Varta OEM battery.



The Motobatt batteries come in a range of sizes, so you should be able to find 1 that fits without any further mod's BUT they are yellow, so out with the rubber paint
Warning! This thread is more than 9yrs ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.