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Any thoughts on a good battery type for my 1974 6 volt bike?
Will be for summer use only so best if it is ok with 6 months zero use.

Regards

Lowest self-discharge you can expect from a

- AGM (absorbed glass mat) sealed lead/acid battery

or a

- LFP (lithium iron phosphate) sealed battery.

For the latter you do not need a different R-R, as the nominal voltages of a 2cell-LFP and a 3cell-AGM battery are nearly identical.
Don't use any other lithium battery except the LFP type! All others have a different nominal voltage (i. e. 3.6, 3.7, ... Volt), do not harmonise with the 6Volt R-R.

https://www.mpoweruk.com/leadacid.htm Info about lead acid batteries
https://www.mpoweruk.com/lithiumS.htm Info about rechargable lithium batteries

Lithium batteries save a lot of weight. At the same electrical capacity, an LFP has less then 40% ofan AGM's weight.

cheers Hans

Thanks Hans,
Lithium Phosphate it is
If I can find any in the UK

Kind regards,
Alex

Hi Alex,

on this page https://translate.googleusercontent.com/translate_c?depth=1&rurl=translate.google.com&sl=de&sp=nmt4&tl=en&u=https://www.kr26.de/el-0250-battery-49.html&xid=17259,15700021,15700186,15700190,15700256,15700259,15700262,15700265,15700271,15700283&usg=ALkJrhgT_jb3g67eDFrUQwQ_4U7efm7QZw DIY manufacturing of a LiFePO4 battery (made from single cells) is described. The page was sent through Google's translator. Unfortunately, the author Thomal Heyl sadly passed away some months ago.
The Headway 38120HP LiFePO4 should be available in the UK as well, together with the necessary mounting brackets.

EDIT:
1) A source in the UK is http://eclipsebikes.com/product_info.php?products_id=90
2) how to build battery packs from LiFePO4 cells: https://www.electricbike.com/diy-battery-pack-kits-four-options-2017/
I solely recommend to use cells with threaded poles, as only these offer reliable contacts between each other, w/respect to vibrations and corrosion

cheers Hans

Thanks Hans,

I am struggling to find a 6 volt LiPo battery here in the UK, custom build could be the way to go.
I see they offer 3.2 v...would a 6.4 volt battery be ok in my Ducati?
Now that it is impossible to get acid to fill dry lead acid batteries I would have thought there would have been lots of LiPo batteries for sale.
Regards,
Alex

The nominal voltage of an LFP cell is 3.2 Volt, the max. (fully charged) voltage is 3.6 - 3.65. So, two cells connected in series form a good replacemant for a 3-cell lead/acid battery. The nominal voltage of a lead/acid cell is 2.0 - 2.1 Volt, the max. (fully charged) voltage is 2.4.
For more information about the differences between lead/acid and LFP technologies you might read this https://www.cycleworld.com/sport-rider/motorcycle-battery-basics-lead-acid-or-lithium/ and this https://www.gliderpilotshop.com/lfp_vs_lead_acid?___store=glider_en article.
All of the batteries containing Lithium are based on electro-chemistry with Li-Ions. But this name is exclusively but misleadingly used for those ubiquitous items sitting in laptop computers, cameras, mobile phones etc. Don't mix them up with the LFPs, as they work under a different chemistry and hence have a nominal cell voltage of 3.7/ max. voltage of 4.2 Volt. We cannot use these in our motorcycles as replacements for lead/acid types.

There are some companies on the market who sell LFP block batteries in various capacities, in 12V as well as 6V versions. A well known manufacturer is Shorai. You might find their LFX18 (6V, 113x58x89mm) also in the UK. In the US, it is offered for ~65$.

Hans

Thank you Hans,

Great information one thing I wonder about is charging lithium type batteries.
Are they a direct replacement or do you have to fit different rectifier/controllers etc?

Kind regards,

Alex

No, you don't need a special R-R for a LiFePO4 battery, as it is a direct replacement for the old lead-acid type.
But beware of using a modern (often micro-controlled9 charger containing a "desulfation" or "rejuvenating" mode. This only works for lead-acid cells, and is performed by applying very high voltage pulses. These will destroy your precious LFP battery, as some battery specialists report. There are dedicated LFP chargers available, or you can use a more old-fashioned charger without that mode.


Hans