CB 500T Electric Issue

Here is the story. Have a 75 honda cb500T. I Just had my mechanic do a clean wire run for all my electrics and install my new light weight battery. His work is very good, and all things look clean, but after 2 short rides yesterday the battery was dead. (I charged it completely before I rode) Here is the diagnostic stuff

After a complete charge last night i checked the battery this am, and the charge was at 14.4

I charged the battery up to complete and it was 14.91

I cranked the bike up and while engine was running cold the charge was 12.75

AFter 2 min it moved up to 12.84

when the bike was warm the charging was a constant 12.74 (with rpm's at 4500), and the headlights on ( i have 2 pretty big headlight both running at low beam )

With the headlights off the volts were 13.0

After 10 min of running I turned the engine off and checked battery and it was at 13.0


This is one of those new ballistic batteries. Super small and lightweight. I already sent an email to the manufacturer and they said that out of 500 sales of this battery 2 have come back faulty.

Do you think my battery is the problem? the charging system? or do I have a wire that is bringing power down

I just checked the battery after its been sitting for an hour, and the charge is holding at 13

I had the same problem with my 76 cb500t I ended up changing the stator. And voltage regulator and it charged again lol.Check ur stator and rectifier also check ur regulator

Also, keep in mind, these old bikes have barely adequate charging systems. If you're running two headlights...that's probably one too many.

Was kind of thinking that about the light. As a quick fix, i pulled the bulb out of 1 light and am going to take a 20 min test run. Lets see what happens

I disconnected one of my headlights, and tested battery. 13.14. I went and rode around town for 20 min and came back and checked battery, and it was 13.84. Problem might just have been 2 lights were pulling too much power

Nice. If I recall, voltage at the battery should be a little over 14v, at 4000rpm. The regulator is adjustable, so if you reduce or increase the draw on your charging system, you can increase or decrease the voltage at the regulator to compensate to an extent.

This is all for a cb550/4, but I'd think it would be the same for the twin cylinder...

how do u adjust the voltage regulator??? i must know lol

Don't recall off hand, but there's a screw you turn under the cover. Do a search on forums.sohc4.net

Remember, as far as I know, this is Honda CB specific, and not a fix for a shitty wiring harness...

the system on your bike will not keep your battery at 14+ volts.
i also have a cb500t and have gone through the whole charging system issue.
on new bikes, charging while revving gets up to about 13v and a tiny bit over if any and 12.4 around idle. i did the check on a 2008 yamaha r1 for reference.
as long as you are getting fluxuating currents from the 12's into the 13's i think you are ok.
i do recommend you only run one stock sized headlight though which only uses like 30w.

i also reccomend swapping out to a solid state regulator and rectifier combo. You can buy an 80s honda one on ebay. i did that, and i also changed my stator and works fine.
or atleast the radioshack rectifier.

hopefully your headlight changes were the problem as that is the easy fix,and it keeps working good, but if not make sure your battery is correct for your bike.
if thats checks out, test your stator with a multimeter.
both currents should be sending 25-60V i believe from idle to rev.

but like i said, hopefully it was just the headlight. ride the hell out of it and see what happens.

i also reccomend a battery tender whenever your not riding, just to be safe.
pm me if you need to if have any other questions i may be able to help with.

Update
I have done 2 20-30 minute rides and checked the battery every 10-15 miles while bike is off. Battery spiked up once to 16, but normally around 13.5 and up to 14. Its looks as though that2nd headlight was too much of a draw. No biggie, i will just wire it to run only on high beams.

I am completely and idiot when it comes to electrics, so all the discussion re: stators, adjustment of voltage, etc. I think I will just leave my mechanic to handle that stuff. I mess up enough stuff as it is. But I would like to upgrade the electrics, just to be on safe side.

Thanks for all the help everyone!

You can run dual lights as long as you change the bulbs to lower wattage. YamahaXS650 has a bad system (renowned for it, the rotor isn't a good design)
However, I've run mine for years with a dodgy battery and dual lights.
I fitted bulbs from 1980's Yamaha 'Genesis', they are 35/35w H4, easily available as a lot of scooters now use same bulb (eBay is cheapest)
45/45 is also available but I think 90w high beam is just too much.
Were you using 60/55w bulbs?
If so, low beam would need almost all of the generator output