CB750 Battery - dying - help


Been Around the Block
I've had to charge my battery numerous times this season. It's a new battery. Holds charge and runs great for about 3 or 4 rides. At which point I usually find myself stuck across town with an engine that won't turn over by electric start and reliant on the kick start to get the bike running.

Today I checked the voltage:
• before installing (12.9)
• while at low idle (12.7)
• around 2000 rpm (13.5)
•above 3000 rpm (14.5-15.8+)

I'm not well versed in batteries or electrical but that seems to indicate at least the charging system is working. I'm not sure what my next step should be here.

It might be important to note that I have a dyna-S electrical start installed many years back.

I've experienced dead batteries in the past but that was more due to long periods of the bike sitting un-used. This is a slow drain during use.

Any advice is greatly appreciated.


BOTM LOSER Proudly Deplorable
Riding from home to the store then to pizza then to get a beer wont allow enough time to charge at low rpm, you need to ride it at +3000 more :eek:


Over 1,000 Posts
Agree with Tuna, if you aren't out wringing some throttle/hitting the highway etc. you're not getting enough charge. Might want to think about a trickle charger if that's the case.


Fuck You.
Have you done a current draw test on your main fuse with the key off? This is critical in properly diagnosing a voltage loss. If not then do one.

Have you had the battery tested?

Most properly functioning motorcycle charging systems break even below idle, meaning they charge at any rpm above idle. Not all, but the vast majority are designed to.

15.8+ volts means what? How high does it go? 15.8 is way overcharging any "12v" battery, and combined with the break even coming above idle rpm actually does NOT indicate a healthy charging system.

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