How to Test Your Motorcycle Charging System


July 10, 2014 | By: J&P Cycles

911-011_ARequired Tools: DC voltmeter or battery tester

As a general rule, modern charging systems are efficient, reliable and maintenance free; however, there are exceptions to every rule and few problems will leave you stranded as quickly as charging system that’s gone kaput. Fortunately keeping tabs on the system is relatively easy; all it takes is a simple DC voltmeter or battery tester.

To start, let’s clear up a fundamental misunderstanding about batteries. Batteries do not create electricity. At least no more than a refrigerator creates food. In both instances the devices are merely storage containers. Both accumulate and return what you put into them. If you use up all the energy stored in a battery without replacing it, it’s as if you’ve eaten all the food in your refrigerator, so until you refill it, you’re going to be out of power or mighty hungry.

It’s the job of the charging system to keep the battery full, which it does by first converting the AC current provided by the alternator to DC (direct current). Batteries can only store and release DC then send that rectified current to the battery at a slightly higher rate than the battery’s standing voltage. Normally a fully charged 12-volt battery in good condition has a standing value of right around 12.6 volts, this can be slightly higher or lower, maybe 12.75 or so, to 12.4 to 12.5 volts, depending on the battery’s efficiency and state of charge, but in round numbers 12.6 is about it. Once the battery charge drops to somewhere around 10 volts you’re done and the engine will simply shut down.

Batteries only accept a charge when the voltage flowing into them is greater than the voltage flowing out.  Unregulated, the average motorcycle-size charging system is capable of pumping out around 75 volts, which is far more than the battery, or the bike’s electrical system can safely absorb. This is where your regulator comes into play. The regulator, which is normally built into the rectifier (some older bikes have a standalone device), reduces the output to slightly more than the battery’s rated voltage. In most 12-volt systems this equates to a normal charging system output voltage of around 14-to 14.75 volts, (however that’s a rule of thumb). The charge rate is dependent on a number of factors, among them the charging systems design, the quality of the components and of course the motorcycle’s electrical demands, so some variation is to be expected.

For example, a small dual sport or commuter bike doesn’t require a massive charging system. As long as the input voltage exceeds the output you’ll be fine. You should expect to see a reading towards the low end of the scale, maybe 13.5 to 14 on a bike like that. By that same token a sport bike, cruiser or touring bike needs a robust charging system, so if you are checking a full loaded touring bike you want to see at least 14.4 to maybe 14.7 volts, especially when all of the accessories are on (you’ve got to love those heated grips and seats on chilly mornings!).

The bottom line here is that you need two things to make your electrical system work. The first is a fully charged battery and the second is a charging system that keeps it that way. The question being how do you know which portion of the system is at fault when there’s a problem?

125-997_AHere’s an example – if your battery doesn’t seem to hold a charge between rides it might be because the battery is on its last legs, or it may be because the charging system isn’t performing as well as it should. So, which is it?

To answer that you’ll need two things: a fully charged battery (no charging system can be reliably tested when the battery’s discharged) and a voltmeter or dedicated battery tester, like the TecMate TestMate mini, which is capable of reading at least 15 volts DC.

Charging system voltage tests are always performed with the battery fully charged and connected to the motorcycle, so the first order of business is to make sure the battery connections are clean and tight. Many charging system problems have been cured after checking the battery connections.

Set your voltmeter to the DC scale, if it has a calibration adjustment set it to read above 12 volts and attach the clamps or probes. If you’ve never used a voltmeter before, here’s how this works. The meter’s positive or red clamp or probe attaches to the positive battery terminal then the negative or black probe connects to the battery ground. A healthy battery should read right around 12.5 volts. If it’s much lower than that, say 12.0 or less, charge the battery before proceeding. If the battery won’t hold a charge, or shows signs of damage, you should replace it.

Assuming the battery voltage is good, start the bike and watch the meter. Depending on the type and efficiency of your charging system, the meter may show only a very small increase or even a decrease in voltage at idle; however, as you increase the engine speed you should see a rise in voltage. At any speed above a fast idle the voltage reading should rise above the standing voltage before leveling off. Preferably you’ll see something like 14 to 14.5 volts, although there are exceptions, so don’t be overly concerned if your readings are slightly higher or lower. If they’re considerably lower or higher you’ll need to take corrective action. For that you’ll need the bike’s service manual and some understanding of how the charging system generates and regulates the current, which is outside the scope of this brief introduction.

On that note, here’s some final advice, if the charging system isn’t working properly don’t ride the bike until it is. I know that sounds obvious, but I’m always surprised at how many guys will try nursing a bike along when the charging system is marginal at best. A dead battery creates all sorts of unpleasant scenarios and if one of them occurs at rush hour on a busy stretch of road you’re going to be in for an interesting experience pushing your bike through traffic, followed by a long wait for help.

The flip side is an overcharging battery is just as bad, perhaps worse, because under the right conditions the battery could literally explode beneath you. Admittedly that’s an extremely rare occurrence and the more likely outcome is that it will blow out your lights due to high voltage, but that’s only marginally better. The bottom line is that being able to determine where the problem is located, will only be half the battle, but at least it’s a half you can fight and win in your own garage.

Comments: 11 Comments | Categorized Under: How-To Articles

Comments (11)

Thank you very much for taking the time to explain to us in a simple way to understand the basics of the charging system. In my personal case help me a lot because I had problems with the charging system in my 1996 Yamaha Virago750 who was consuming the charge because the battery didin’t hold it. Thanks again

Thank you for sharing this great article!

Alright I recently bought a 2009 kawasaki ninja zx6r monster edition with 11k MI in excellent shape only mods are frame sliders as two brothers exhaust. I have put 800 miles on the bike with no problems, however I took a 40 mile trip today and ended up stranded on a off ramp and before completely dying the bike began to studder and starve for fuel and all instruments wentry dead and finally died. I first tried to restart the bike and had a obvious dead battery so I walked to Walmart a mile away and bought a new battery, had it charged and in sales it in my bike and it fired right up but found myself 20 minutes from home with the same problem, let it sit for 20 minutes and it started so I rode it home. I charged the battery and tested the voltage with the bike running and charging system will work initially and then stop and begin to drain the battery, shut it off restart and no charging so what is faulting out and preventing the battery from being charged?

Your REgulator is faulty like mine. it overvoltage, and over charged resulting to drained battery

I let my bike (2000 HD Road King Classic) sit all winter and the battery is dead. I tried a trickle charger but it’s not enough. Time for a replacement?

I have an 05′ 1200 sporty custom this is long horror story I’ll try an be brief, Last year electrical issues led to bad stator. Replaced stator battery voltage reg. Bike ran fine this spring started having issues again narrowed it down to stator again! Took it apart again to find out stator good but voltage reg.out again. Got new one problem solved for about half hour bike completely drained and died voltage reg shot again. Bad ground can’t seem to find that problem. Getting tired of throwing 100$ away like its nothing. Question: last year on a run my key chain with the alarm gizmo thingy broke off keychain and gone no idea where. Okay about three weeks later lost ignition key. Put trust in friend when he had a ignition from something else , after all it worked and still does turns out it’s from a little 48cc scooter. Is this my problem cause nobody can figure this issue out and I’m ready to light a match on my bike it’s driving me bat shit crazy!!!!! Please help thank you !!!!! Matt Baer


I would definitely change out the ignition switch. After that, if the problems persist I would trace grounds. If you can’t find it, it would be worth spending an hour labor for a tech to diagnose.

J&P Cycles

Dose any one know how to test a 2007 street bob charging system as I can’t seam to put my finger on the problem bike starts fine first go but on the 3rd it dose not have a enough to start it but battery is not fully flat still turning motor but not enough . All so once bike has been for a quick ride or is hot same thing will turn motor but not enough to start any ideas ?

on my old triumph mc and my father’s Silverton cabin cruiser there was a gauge for ampheres. 0 in the middle with a negative scale to the left and a positive scale to the right. This deal told you at a glance if you were charging or discharging. I counted my blessing with this baby with the triumph as it saved me many long pushes.rectifier under seat went bad all the time. Would really love to have one on my 82 fxe. you folks should try and find one to offer your customers. I’d buy it immediately.

[…] lot of the electrical components including the $500 ECU Here is an article that might be of help:…arging-system/ BTW, if under warranty just contact them with the code and arrange for a […]

love the analogy with fridge full of food. never heard it explained like that before, very entertaining. keep it up…

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