Nobody wants to be stranded by a bad battery on a trip. Some just replace their batteries after they've reached a certain (arbitrary) age, perhaps wasting a battery that may have years of life left in it.
A load test is the common man's best way to determine the condition of a battery.
I like to do one on my battery about a month before leaving on a long trip. If the battery fails, this gives me enough time to order one from Hal and perform the swap before the trip.
Here is how I do the load test the OEM Yuasa battery in my bike (my bike is in my signature):
To do it like I do, you'll need a few basic hand tools and a load tester. A digital voltmeter is desired, but not required (assuming the load tester unit has a voltmeter). A laser (or IR) thermometer is also handy to have.
Here is the load tester I use:
500 Amp Load Tester
I've had it a few years and am pleased with it. They go on sale from time to time for about 20 bucks less.
Let's get started:
First, you need access to your battery. Remove the port side cover. This just pops out, but be careful not to damage the cover.:
You will now see the battery. Remove the trim clip holding the black plastic battery cover plate in place, then remove the black plastic battery cover plate:
Next, remove the battery holder bolt (use an 8mm socket):
You can now move the battery holder out of the way.
The first thing you will test is the battery's unloaded voltage. I first burn off any "surface charge." This prevents the battery from indicating an unrealistically high voltage. Remember, you are stress testing the battery, not preparing it for a beauty pageant. If it's gonna break, you want it to be in your garage, not 30 miles north of Sierra Blanca, TX.
To burn off any surface charge the battery may have, turn on the bike's ignition and select the high beam headlights. Let 'em burn for three minutes:
Just for S&G's, I like to monitor the battery voltage during the three minutes the headlights are on:
What you want to see is an initial voltage drop followed by a steady voltage indication. (For this test, my battery dropped quickly from 12.62 v. to 11.68 v. and then remained at 11.68 for the remainder of the three minute period). If your battery voltage keeps dropping for the three minute period, you may have a problem.
After three minutes, turn off the ignition and then wait for five minutes. Measure the battery voltage after the five minutes have elapsed. My battery indicated 12.56 v., which is fine. If you see less than 12.21 v. after this procedure, you will need to fully charge the battery and burn off the surface charge again before proceeding any further.
You will find a chart of voltages and charge levels on this page:
(Scroll down to the bottom of the page.)
Here is another source of good info about Yuasa batteries:
You are almost ready to run the load test. But first, you will need to know the temperature of your battery. To get a rough idea, you can use the temperature in your garage. I use my laser thermometer and get a reading off of the battery case. Write down the temperature.
Next, I remove the battery cables from the battery and pull the battery out far enough such that I can get the load tester clamps on the battery. The black clamp goes to the negative terminal and the red clamp goes to the positive terminal. I also position the test probes of my digital voltmeter on the terminals so I can read the battery voltage as the load test is being conducted:
Here is my load tester:
Here, you can see the clamps on the battery terminals. We are now ready to apply the load to the battery:
Next, I quickly twist the load knob on the load tester until I get to 135 amps of load on the load tester's ammeter. (I use 1/2 of the battery's cold-cranking amperage rating of 270.):
(The OEM battery is the YTX20L-BS.)
After the desired load is attained, I count 15 seconds. You can count, use a watch, or use a timer. My load tester sounds a beep after 15 seconds, also. While the 15 seconds are ticking away, I keep a weather eye on my digital voltmeter and note the lowest voltage seen. It is normal for the voltage to drop slowly during the load test.
After the 15 seconds have elapsed, I remove the load using the load knob and disconnect the load tester terminals and digital voltmeter probes from the battery. You may notice a "hot electrical" smell coming from the load tester, this is normal. The case will probably warm up some, also, after the test is completed.
OK, you've now got the two pieces of data you need to determine the battery's condition.
Although the voltmeter built into the load tester has indications that tell you whether the battery passed or failed the test, I like to use the table in this reference:
So, using the chart in the above reference, I see that my battery passed the test. The measured battery temperature was 40 deg. F and the lowest voltage I saw during the 15 second test was 10.23 v. All I needed to see was 9.3 volts, so my battery passed with about a 10% margin.
You've just stressed your battery, so it is important to recharge it fairly quickly to prevent deposits from forming. I hit mine with a 1 amp charger for about an hour or so.
Reinstall the battery cables, button everything back up, and you're done.
By the way, you may find it useful to keep a log of test results as your battery ages. I first load tested mine three years after I purchased the bike. The battery passed with a margin of 30%. Six months later the margin had dropped to 16%, and now (four years after I purchased the bike) the margin is 10%. I'm pretty certain this battery will get us through our upcoming 7000 mile business trip.
Here are the economics of load testing your battery vice just replacing it every three years (note, however, that I've had several motorcycle batteries not make it to the three year point): Hal wants $104.00 for a new battery (not including shipping). If you get a battery every three years, you spend about $35.00 a year on batteries. I got this load tester on sale for about 30 bucks. Because of it, I've been able to keep my battery for four years (and counting). The load tester has thus paid for itself in one year and I've got an extra $5.00 (and counting) in my pocket to boot.
Multiply that by my five motorcycles and it's better than wages!
However, more important than the economics is the feeling that you're departing on your trip with a strong battery that will get you back home!