Battery Testing?

Special for @unofix?😃
Dan talks about battery testing and explains why modern cars are very hard on them (Start to 8:15):

Whilst the Midtronics tester he uses (Ford also won't accept anything else for warranty AFAIK) tests "RC" (Reserve Capacity - it's capacity in Ah that usually let you down and can't be measured easily)

Remember they only guarantee against manufacturing defects (1 year from new, 3 years if you buy the same battery as a spare from them - well. that's my experience!

They DON'T warrant wear and tear unless you object a lot and are really lucky!
However, I measure capacity using the process described here (it's for caravans, where leisure batteries  are used and you really need capacity):
Fully charge, discharge using headlamp bulb, measure current and voltage taking readings every half hour until the voltage drops to 10.5 ish. Immediately recharge. Calculate capacity from the sum of each half hour's average current & time readings giving total capacity in Ah.

Battery University is, IMHO, an excellent source of info and gives the aging process here:
https://batteryuniversity.com/article/bu-806-tracking-battery-capacity-and-resistance-as-part-of-aging
As it gets to 40% capacity, you may have another year... or not so change it?

Whilst voltage is one really important parameter, it can't tell the whole story, batteries are like people, they fail in multiple ways (no good the doctor testing your reflexes if you have high blood pressure?)

Edit:
This is also specific to testing:
https://batteryuniversity.com/article/perception-of-a-battery-tester
Anyway hope this is interesting and adds knowledge?

Edited January 3, 20251 yr by Shearers
Added testing link.