Join Date: Feb 2017
Location: St. Louis, Missouri
Regardless of what Yuasa prints out--and I use Yuasa batteries in my bikes exclusively, testing rest voltage doesnt really give you the info you need to judge a battery.
In a flat-rate situation as I was in for 43+ years, I didnt have 20 minutes to test a battery, much less 2 hours.
Which is why I use testers to check the battery internal resistance. Typically, a car good car battery will have around 21 micro-ohms resistance, a good motorcycle battery will show around 7 micro-ohms resistance.
The tester uses this resistance reading to compute the current capacity of the battery. This capacity is the main point of interest.
The Yuasa catalog shows the battery and its rated Cold Cranking Amps. CCA is rated at 0 degrees F. Since I dont ride at 0 degrees, that number in itself means little, but I can use it for comparison testing.
For example The battery in my '14 DL1K is a Yuasa YTX-14BS, rated at 200 CCA. In AGM Battery testing mode for this specific battery, I measure 268 CCA, well above spec. My other tester tester reads 10.0 micro-ohms. This battery is 21 months old, has 7K miles on it, sits on a Battery Tender when not in use, and gets ridden regularly.
Another test is a dynamic instead of a static test: Battery fully charged, ignition and/or injection disabled, crank the engine for 15 seconds. The battery voltage should not drop below 1.0 VDC during crank.. A carbureted bike, disable the ignition and voltage during a 15-second crank should not drop below 9.6VDC.
The Yuasa test is similar to my Snap-on testers, much less expensive, and will tell you what you need to know.
With regular testing, a low reading even during what appears to be a normal cranking speed, will allow you to make your battery plans accordingly instead of cussing yourself or the bike out on the side of the road.
And even with all that, and meticulous maintenance... the battery decides when its number is up.