6v lithium battery NGC

[steven c]

 Will I run into an issue by using a 6 volt lithium battery in my 78 Honda XL125? Could there could be a charging issue with the Honda's  primitive system?
https://www.amazon.com/dp/B09WYF8GP7/ref=sspa_dk_detail_6?pd_rd_i=B09WYF8GP7&pd_rd_w=usGHm&content-id=amzn1.sym.953c7d66-4120-4d22-a777-f19dbfa69309&pf_rd_p=953c7d66-4120-4d22-a777-f19dbfa69309&pf_rd_r=TYK7S8TJHB64JBGQ37KF&pd_rd_wg=xxVkt&pd_rd_r=a8297aa3-cbb4-4564-9b04-edb3cdafbb31&s=automotive&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWwy&th=1

[DoubleGuzzi]

At a minimum, I'd connect a (5A fused) cheap voltmeter to the battery, to closely monitor the output whilst the engine is running. I wouldn't want to see anything above 7.4V, as a close guideline. (Unless calibrated a voltmeter will have inherent measurement error - expect up to +/-0.2V .)

From the advert:
" Charging Voltage    7.2±0.2V "
I note that graphs illustrate performance curves for a 12V battery!
Also, this is disconcerting:
"Peak discharge current    12A (Duration: less than 5 seconds) "
No electric starts then. 

[steven c]

 Kick start only. Volt meter is a good idea.

[DoubleGuzzi]

Kick start only.

I do know that, of course. Great wee bikes those XLs. 

Let's see a pic of the XL Not so much the Benelli, 'cos you'll make me even more jealous! 

My favoured item:
https://www.aliexpress.com/item/1005005096647903.html



Either make a small bracket or stick on with black bath sealant.

[steven c]

A real barn find, had under 300 miles on it when I bought it.

[DoubleGuzzi]

A real barn find, had under 300 miles on it when I bought it.

Wow! Time capsule.
 

[steven c]

 After reading this I will not be putting one in unless I could upgrade the charging system.

https://forum.antiquemotorcycle.org/bboard/forum/general-restoration-discussions/electrical/18799-your-thoughts-on-lithium-batteries-in-vintage-bikes

[DoubleGuzzi]

Interesting and my warning to closely monitor voltage is confirmed.
A relatively cheap device:
"Kokusan / universal voltage regulator 6V"
(Kokusan ignition units were used in carb-based Ducati Monsters.)
 

[SIR REAL ED]

After reading this I will not be putting one in unless I could upgrade the charging system.

https://forum.antiquemotorcycle.org/bboard/forum/general-restoration-discussions/electrical/18799-your-thoughts-on-lithium-batteries-in-vintage-bikes

A wise decision.

I can't imagine any advantage to a lithium battery in that bike.

IIRC, a lot of the bikes from that era run fine, even with a lead acid battery that has been dry for years.  Hard to remember even seeing a bike from that era back in the day that didn't have a lead acid battery that wasn't bone dry.

[DoubleGuzzi]

^ LOL.
Yup, a proper working battery was optional. 
The standard battery won't weigh much anyway: perhaps use a gel one if available, for reduced (zero) maintenance.

[antmanbee]

After reading this I will not be putting one in unless I could upgrade the charging system.

https://forum.antiquemotorcycle.org/bboard/forum/general-restoration-discussions/electrical/18799-your-thoughts-on-lithium-batteries-in-vintage-bikes

I'm not sure I would draw a conclusion from the info in that thread. It is 8 years old and it looks like they are talking about Lithium Ion which is used in phones, and not Lifepo4 which is what is used in modern motorcycle batteries. Also a battery should have a BMS that should cut off the charging either when the battery if fully charged or if the charging voltage is too high. It should also have a low voltage protection. Lifepo4 is not known for bursting into flames.
I am not familiar with the 6V charging systems and regulation, but I would do more in depth research before ruling it out.

[steven c]

A wise decision.

I can't imagine any advantage to a lithium battery in that bike.

IIRC, a lot of the bikes from that era run fine, even with a lead acid battery that has been dry for years.  Hard to remember even seeing a bike from that era back in the day that didn't have a lead acid battery that wasn't bone dry.

it has a higher amp's which I thought would help with my turn signals flashing at low RPM's. They don't, yes I have a  new flasher relay.

[DoubleGuzzi]

Non-flashing indicators ain't that uncommon on 6v bikes, IIRC. That certainly seems like a cunning plan: alternatively, I wonder if 6v is enough to drive LED indicators, whereby the lesser resistance should help. Not something that I've even thought to look into. 

[Dr. Enzo Toma]

Many early 6V Hondas do not have a voltage regulator so the battery is used to absorb spikes in stator output and prevent the light bulbs from popping. I would check to see if that model has one or not, and if it's in good condition. Without a voltage regulator, you can obviously dangerously overcharge a 6V lithium battery. That said, I run lithium batteries in some of my vintage 6V bikes that have voltage regulators. They're great for bikes that rarely get ridden because the self discharge rate of lithium batteries is low so you can park them for 3-6 months without needing to plug in a lithium battery compatible charger. If the bike doesn't have a voltage regulator and even if you go with something like an AGM battery, it's a common mod to put a voltage regulator in front of the headlight as those 6V bulbs get pricey if you keep burning them up.

Running a removable 6V lithium battery just for lights is another idea, and common with LED replacement on vintage bikes that see rally use (Motorcycle Cannonball events). Batteries Plus sell 6V rechargeable Duracells that are the common choice.

[steven c]

Can a voltage regulator be added to a vintage 6 volt system without one?

[DoubleGuzzi]

Can a voltage regulator be added to a vintage 6 volt system without one?

Yes. I gave you a clue what to search for.
A little more explicit, with no recommendation/experience:
https://rexs-speedshop.com/product/universal-6-volt-ac-regulator
https://www.wemoto.com/bike/honda/xl/125/1975/19590/regulator
I do note the following from a relatively expensive manufacturer:

Electrex World regulator/rectifiers MUST NOT be used with Lithium-ion batteries.

One assumes this isn't applicable to LiFePO4 batteries.

[steven c]

 Seems like a fair warning.

[Kiwi_Roy]

Can someone post a link to the bike's wiring schematic.

[steven c]

https://www.xrv.org.uk/threads/1978-honda-xl125-headlamp.145273/

[DoubleGuzzi]

..1978-honda-xl125-headlamp.145273/

There's your answer:
The battery is charged (and the main power supplied) through only a silicon rectifier, which according to the diagram is just a diode - half wave rectification and no regulator. This hypothesis is reinforced by the use of that headlamp resistor, which helps prevent the bulb blowing due to excess power.

IIRC, my SS50 and my now wife's YB100 was similar, whereby indicators slowed/dimmed/stopped flashing and lights dimmed, whenever sat at idle. Not good when waiting to turn across traffic at a junction! A spot of revving was required. The joys of 6V electrics.