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Replacement Battery Advice

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The old 12 volt lead/acid battery on my Dommi 99 has died after 5 years and I was wondering if replacing it with a modern Li-Ion or AGM battery. Is this a realistic option for bog standard 1960's bike or not? 

I've had modern bikes with AGM batteries and obviously the modern bike is designed for these types of battery.

Any advice gratefully received. 

John

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AGM is what I use, Li-Ion needs a different voltage regulation which AGM does not and you get the advantage of no leaks and so far long life.  Li-Ion are at risk of spontaneous ignition.

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My 1959 99 is fitted with a Varta sealed 12v 6AH 50(a) YTX7L-BS. Its been on the bike at least 4 years and there have been no problems. I think this maybe broadly equivalent to what it was fitted originally as don't want to complicate things with more modern items given my lack of knowledge in case I cause problems and it seems to have worked. The bike has stood inevitable given today's pandemic without use for about 9 months yet only a slight drop in charge. I think it was 12.5. Topped it up last week on charger as it happens and it is holding 12.85 volts. Not sure of the cost of the batteries you propose but replaced my Royal Enfield battery although magneto model with the same battery for about £30 earlier this year as this was about 7 years old given this experience. Trust this helps. Regards, Hugh   

 

 

6Ah sounds a  bit low.  Why not go for this at 12Ah.  Should be good if you had a bike with a starter (Not the 99 obviously)

Ultramax Yumicron YB14L-A2, 12v 14Ah

This was with just a quick Google search.  The greater the battery capacity the better  - provided it fits the box!

I can't get the link to load up properly so just search that model.

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Sorry Lionel, but why pay more for a big battery and lug the extra weight around? 

It isn't as if there is a huge electrical load on a 99 and it is a kickstart only bike so to my mind a big battery isn't required either, unless you want to park it with the side lights on all night.

Provided that the wiring and alternator are in good order, then the alternator will more than balance the loads put on it. A 7ah battery should be perfectly fine on the bike. 

Regards, George. 

(Ps: I have a 7ah on my 650 and have no issues due to battery size)

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Why pay more for a big battery? I'm a pessimist; if the charging system goes down you've got more range to get somewhere convenient for repairs. (On the other hand, I'm a real pessimist; you also have the ability to travel further away from sources of help … )

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If you run a  basic charge control system a bigger battery   is able to  cope with   the  high's and lows  a bit better.   Mine has enough guts to power a compressor  to pump tyres and  toast me  with a short blast of a 70 watt  jacket.   Once warmed up  25 watts   is enough. The rest gets used on electronic ignition,indicators, sat nav, chain oiler and heated grips. I usually run daytime lights . Don't think the zener gets a look in,but the  rectifier  has a big heat sink and i carry a spare.

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An equivalent to the 2MC capacitor you can remove the fuse after the battery fails and continue home. 

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Hi John,  You are going to have to expand on that ,  I'm left behind !   I think the 2MC is still availiable , I still use one and yes,my bike starts and runs without a battery , A couple of miles up the road I realized  it was still on the bench !!. The ampmeter went beserk.

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Thinking about charging issues,  My rectifier is probably working close to its max, is there a HD version or can 2 units be used in some way?.  Alternatively I could adopt the easy rider position and warm my boots on it.

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Robert, any BSA wiring diagram for 1970 has the 2MC capacitor as an option, its also in the Commando wiring diagrams at least for 72 to 74. Do not fit a NOS 2MC as they are destroyed by age, modern capacitors do not. If your battery fails by going high resistance you have to pull the fuse for the capacitor to work, if you do not then the battery sucks all the electrons for itself.

 

Starting in 1968 Triumph and BSA sold only “road” bikes with the battery/coil ignition. If you wanted to ride off-road or race you were forced to buy a road legal motorcycle, remove the lights and otherwise prepare it for competition. Part of that preparation included removal of the battery and battery tray. The battery, which was required for proper functioning of the battery/coil ignition, was replaced with the Lucas version of the ”battery eliminator”, otherwise known as the 2MC capacitor. The 2MC was a large electrolytic capacitor that connected to the harness in the same manner as the battery, but weighed about 1/100th of the battery. Starting in 1968, Norton P11’s also came from the factory with a battery and a 2MC capacitor fitted. Again, the P11 was a competition machine and most P11’s ended up with the battery removed. Then, starting about 1970, all Commandos came fitted with a battery and the 2MC. By installing both, Norton was able to hold the system voltage at high levels even though the battery may have started to age and slip below 12V.

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I also have a couple of reasonably modern reg/recs  that I intended to fit to my 99 and as a replacement for one on the Ducati thats fried its alternator, however  i'm hearing that some replacement alternators are failing after a short life and  there are newer designs of  regulator that are better  . So I'm not fixing  whats not broken,and waiting for  clarification.

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After reading the above more relevant replies it looks like and AGM battery is the way to go.

Thanks for the comments.

John

 

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I bought an AGM battery for the car by mistake ,the main dealers said it would invalidate the car warranty as the charge system was not compatible . Don't think I fully believed them.

Firstly a 6Ah battery is puny and below the original spec.  Secondly there is little or no price difference. Thirdly I can't find any info on their respective weights, but I suspect it is insignificant.  Fourthly the bigger capacity will give you a better reserve if your charging system goes belly-up or if you want to run anything else from it e.g. SatNav, Phone charger etc.  

It's really a no-brainer!  AGM batteries are similarly low on capacity so I wouldn't bother with them.

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Lionel can you advise what the original spec  for the battery to be fitted to a 1959 99 if 6ah is too puny was as have been looking but can't find anything. Thanks. Hugh

 

 

 

C

 

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I’ve had no problems with AGM batteries and would recommend them over conventional sealed lead acid. The main advantage is they seem to last longer with needing a recharge. I use a standard Yuasa 12v battery charger. I have Motobatt AGMs on all my bikes including the Commando and Dommie.

HUGH -

It was the Lucas PUZ7E which was a 12 Ah battery at the 10 hour rate.  I'll try to post a snapshot of Lucas Battery data here.  As you can see that's twice the power of the battery you mentioned. 

It was of course a 6 volt battery - the way I'm going with the restoration of my 1959 99.

 

 

In answer to Robert Tuck in February.

I doubt your rectifier is near its limits, I have never known such on a British motorcycle. BUT I do sell a relatively bomb proof rectifier. You cannot use two rectifiers together with any success.

I seem to recall reading in MCN many beers ago about Norwich Union's infamous "Original Spec" requirements so as not to invalidate the policy. Problem being, they refused to divulge what in their eyes constituted non-OE, and riders were subsequently having claims thrown out due to a bike having silly changes, like a different brand of spark plug.

Don't know if it's still the same...

Funny you should say that AGM batteries are low on capacity. I have one on my electric start Mk3 and it works.  I just googled the question and an AGM battery should be actually lighter comparing like for like with a flooded cell battery   

I take it  back!  Tayna list a 13Ah 6 volt battery, although I can't see the discharge rate characteristics.

 

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