Does size matter? Batteries that is

Previously wrote:

The stock Commando battery is 14A/h The question is, why does it have to be that large if I don't have electric start? I have a three phase alternator and Boyer power box, Boyer ignition. As I see it, all the battery has to do is power the ignition until the engine is running then the charging system will do the biz, unless I want to park with the side lights on. (haven't done that in the last 40 years) Can I therefore fit a smaller and hence cheaper and lighter battery?

Dave.

Of course you can - and then the day comes when you find it's stopped charging and you are still 100 miles from home... Gordon.

A look around and you will see that there are modern batteries that are smaller in dimension with more cranking amps than the original spec, ideal for MKIII. Mind you being an ex-diesel Submariner, I will stick with Lead-Acid whilst using a dodgy old rectifier and Zeners. I will upgrade when I fit a more precise rectification control or powerbox.

Given the above, what is the recomendation for a replacement battery for my non E/S Commando (72 850 MkII A)? I used to fit Yuasa burglar alarm batteries for years - which were excellent along the lines of chris grimmett's experience. I only really started worrying about this when I bought one of those replacement ignition warning lamps that come on when you have less than 12 volts in the battery - so it comes on when your revs drop below about 2k. With the smaller battery, and with headlight on, I would get the red light on quite a lot, particularly when indicators selected and very bright when braking as well! I realise that I shouldn't necessarily worry about this, but I find it disconcerting to see red lights coming on when riding. So I was persuaded to the larger battery - a Unibat cb14l-a2 at huge expense - and marvelled at how well my indicators worked! But that battery has now failed completely after only about 18 months! It's probably done less than a couple of thousand miles and kept on an Optimate charger when parked for any length of time.

So I need a battery that will keep my idiot light off (so the 14Ah I think) but one that'll last a little longer than my last experiment!

Hi David - I've been using a 'burglar-alarm' Yuasa 7aH battery on my Mk2A for about 9 years without problems - I have a 3-phase alternator and Boyer Power-Box (as you do - ) and it's been fine (still on the same battery - - )

I agree the Yuasa 7aH used to last me very well, but I did get the red light problem on a lot with the voltage/ignition light, and the indicators did run awfully slowly at times - reduced to switching them on and off to pass MOT tests etc!

I wonder if they do a bigger version of the old 7aH which might be worth a look?

Previously wrote:

Hi David - I've been using a 'burglar-alarm' Yuasa 7aH battery on my Mk2A for about 9 years without problems - I have a 3-phase alternator and Boyer Power-Box (as you do - ) and it's been fine (still on the same battery - - )

Just discovered that Yuasa do a Y9-12 Yucel. At only £17.99 it may be a good compromise? Does anybody have any experience of this battery? My alternator is a so called heavy duty one, but not 3 phase. I also have the Boyer magic boxes installed, and the aforementioned Al Osborn voltage light in place of the original ignition/charging light.

I think my success criteria is a battery which has enough capacity to run brake lights and indicators to a good standard (not forgetting head and tail lights of course!) without instantly causing the red light to come on below about two and a half thousand revs. Is this technically unreasonable?

Previously wrote:

I agree the Yuasa 7aH used to last me very well, but I did get the red light problem on a lot with the voltage/ignition light, and the indicators did run awfully slowly at times - reduced to switching them on and off to pass MOT tests etc!

I wonder if they do a bigger version of the old 7aH which might be worth a look?

Previously wrote:

Hi David - I've been using a 'burglar-alarm' Yuasa 7aH battery on my Mk2A for about 9 years without problems - I have a 3-phase alternator and Boyer Power-Box (as you do - ) and it's been fine (still on the same battery - - )

Had this same problem with my MK3, I measured the current draw from the battery when this happening and even though warning light was starting to illuminate, there was actually still current going to the battery not from it. I now know that it still charging and thus I'm not to worried about it glowing at lower revs or at night.

I have noticed recently that some of the 'Alarm' style batteries are being used forchildren'stoy cars etc. They are deep cycle ones and I suspect they are fine for motorcycle use, they look just like alarm batteries. The Austrians have been using these cheaper, smaller, lighter Yuasa batteries in their Puch SV and SGS and there seems to be little if any mention of failure of them.

A few more thoughts to above. 14Ahr or 8Ahr are both satisfactory bearing in mind the bigger gives you more reserve. What is taboo is to go below 5Ahr as with such you could easily be into an overcharge situation simply by riding for several hundred miles. Also the use of dry fit 'alarm batteries' If you examine the charge/discharge specification of these batteries you will see that discharge is fine but your crude bike charge will tend to overcharge very easily, hence the battery will dry out sooner than you would like it to. I feel you 'are getting away with it' Buying a battery 'for automotive usage' is to be recommended.

Al Osborn.

I am not familiar with the Commando warning light, having never owned one, but going from my more extensive experience with cars I would expect a red light when there is a net discharge as Chris says. This should be where the load is greater than the charging. It would be the same regardless of the size/capacity of the battery - even if it was the size of a house! A larger capacity battery would have the capability of lasting longer under discharge conditions, alsoas Chris says. It's all down to the charging system.

The rectification and charging control needs to be fairly sophisticated if you are using gel burglar alarm batteries as Al says. This could be why David's failed after 18 months. A normal bike rectifier would allow the battery to cook because of too high a voltage, and current probably. Optimate and other "intelligent" chargers are able to cope with these types of batteries.

Cheers, Lionel

Hell all,

Optimates might be fine to keep a battery up but it will not bring a flat battery up. Be aware. If you must use other than an Automotive battery then I would suggest you investigate your specific (non automotive battery) batteries charge characteristic and then look at what you are doing. A large 'dry fit battery can possible cope with your motor cycle 'casual' charge methods.

If you have a low speed 'lack of electricity' problem then that is the charge systems capability as above. If you must use the above dry fit batteries then usage of lights all the time will reduce the availability of excess charge so you might be safe.

While muttering on about these things, the modern regulator/rectifier might have better battery charge voltage than the 'good ol' zener diode /rectifier. but you might not. The Zener/rectifier system is still an adequate system and is not specifically any less efficient that the reg/rect. The snags with the Zener system can be-old wiring and connections=losses. The Zener Voltage is very variable, a low one gives you a poorly charged battery, while some give over voltage. (say over 15V could very well give you a well charged battery (possible a better low speed result as well.) I have seen reg/rects giving low voltage as well. So get your multimeter to work if you have any doubts but BEWARE cheap digital multimeter suffer from ignition interference so the chances are you cannot measure the charge voltage anyway!

Have fun, Al Osborn.