Not only old cars, but sometimes because of the lack of recharge due to the installation of many electronic accessories, accidentally causing the engine to fail to start, there should be many knights with this experience. Let us understand here that even a cheap tester can confirm the “basic principle of charging circuit”, which is extremely important for charging systems!

Translated article authorized to reprint from: Webike
Original reference:[DIY small classroom]Use a voltmeter to measure whether the vehicle electrical system is normal

Before starting the engine, check the terminal voltage of the battery. If it has a voltage of 12.2 ~ 12.4 volts, it may be safe, but if it does not reach 12.0 volts, the battery is insufficient.

It can be checked with a cheap tester!

Nowadays, there are various brands of circuit testers on the market. It is best to refer to the user’s sharing when choosing; if you like motorcycle repairs, you must at least prepare several different types of testers.

There are many ways to extend battery life (mentioned later), but the easiest and most common way is to use a charger, which allows you to “plug the charger in” when not riding or storing.

Plug in the charger after traveling home, so that the charger can diagnose the status of the battery and charge it as needed. A high-performance battery charger can guarantee the best condition when you want to ride. It is definitely a “good ally” for motorcyclists.


  1. Before starting to use the battery, it is necessary to fully charge the new battery.
  2. Remember, if you use it without charging, the battery life will be shortened in the future.

Let’s compare the battery voltage under various conditions

When the engine is stationary, the charging circuit usually works during idling, resulting in a higher voltage (even foreign old cars will not charge at idling speed). As you can see, the voltage rises when the engine starts.

When the engine speed increases, the voltage rises to 17.10V! Compared with the idle speed, it has risen by about 4.7V. In other words, the charging voltage will increase with the engine speed, but… this change value is obviously overcharged!

KAWASAKI Z in the air-cooling era has many overcharging problems

The problem of overcharging is more important than the problem of low charging voltage. The KAWASAKI Z in the air-cooled era has many such problems. Due to the failure of the regulator, the high voltage is caused and the battery fluid is dried.

“Overcharging” is the most common cause of KAWASAKI Z1/Z2 electrical system problems. High-speed operation under abnormally high voltage will cause the battery fluid to dry out and spray out from the respirator, causing the battery casing and other nearby components to rust and exhaust. The chrome layer on the tube also came off. The countermeasure component for this problem is a voltage stabilizer/electrolyzer sold in specialty stores.

At that time, there were KAWASAKI original parts for the rectifier used to convert alternating current to direct current and the regulator for controlling the voltage. Checking whether the charging voltage has risen is the most basic thing, but even if the voltage rises, the charging conditions will not improve, unless you use the appropriate “current” to charge. Sometimes due to the aging of the line, even if the voltage rises, the current value will not rise, so the current value must be measured. With the DCA (Direct Current Ampere) clamp tester, which was not available when the old car was born, diagnosis is easy.

Here, we only checked the current charging status, but this check found that the voltage regulator has been broken and overcharged. In this situation, I want to replace it with a modern high-performance regulator/rectifier before it is damaged. This is an essential maintenance.


  1. Using countermeasure parts sold by used car dealers, the condition of the electrical system will be improved.
  2. At that time, too much adherence to the original parts will lead to an increase in the failure rate, which is one of the indisputable facts.