Home-made battery checker.

[GHA]

I found I need to do this for my bank as I probably have a bad battery/cell.
Going to follow this guy's suggestion, cheap and doesn't rely on me being around to watch it.
https://www.youtube.com/watch?v=W-g6SGEXEfY

Good find

Though watt meter just records up to 65Ah, maybe it cycles back to 0 & starts again.

 

[ottow]

Point, but given that one shouldn't discharge a lead-acid battery past 50% or so I expect it to work for my 80Ah batteries.
There are other, similar watt meters that can record higher Ah values.

My batteries passes a load test just fine, but it seems the capacity is way down. If anyone of them is in bad shape I expect the voltage cut-off to trigger quite a bit earlier than expected.

 

[GHA]

Point, but given that one shouldn't discharge a lead-acid battery past 50% or so I expect it to work for my 80Ah batteries.\

Should certainly give you a good idea what's going on over time, streets ahead of most, though the battery capacity is normally given as a 20 hour rate, at current draw of capacity / 20 down to 10.5V - so 200Ah battery should be able to deliver a 10A load for 20 hours before pulling the voltage down to 10.5V. If it's straight back on the charger then discharging to empty generally seems to be considered OK once in a while by those in the know.

 

[Birdseye]

I should change at least one of my boat batteries this year, maybe more.
I date mark them, but that doesn't guarantee that the oldest is the worst.

Can I devise a home made battery checker to decide from the three batteries which should be changed? Something that measures volt drop under a reasonable (say 20A) load perhaps? Suggestions?

Easy enough. I use a car headlight bulb in a socket with two wires and plot the time taken for each battery to fall to approx half charged from full - say to 12.2 from 12.7. You can do some crude maths to work out the effective capacity remaining and therefore how much of its original 80aH the battery can now hold.

 

[ctva]

I have three 55Ah batteries. They're set up in a bank of two and a single. They are 2005, 2007, 2009 vintage. Not bad life I think! ...

At that age, I'd not waste my time testing them and just replace all three.

 

[jwilson]

Easy enough. I use a car headlight bulb in a socket with two wires and plot the time taken for each battery to fall to approx half charged from full - say to 12.2 from 12.7. You can do some crude maths to work out the effective capacity remaining and therefore how much of its original 80aH the battery can now hold.

The one time I did this with a 55watt bulb on one of a pair of 70AH leisure batteries I was truly horrified how little AH it took out of the battery to get it from a fully charged but resting 12.7 down to under 12v. Didn't bother to test the other of the pair, just bought 2 new.

I know a set of true deep cycle batteries would be much better, but no easy place to fit them without structural alterations.

"Services" use leisure batteries tend to have a short life if given any real work: starter batteries used just for starting and a windlass last ages, just like they do in cars. Sold a 12 year old Volvo with what was definitely the original battery in it - not long before I sold it the battery was tested and the fancy electronic tester showed CCA almost exactly as the label said - about 900A.

 

[GHA]

You can do some crude maths to work out the effective capacity remaining and therefore how much of its original 80aH the battery can now hold.

Certainly learn something, but so many variables any figures could well be miles out, or quite accurate, and you won't know which....

Though if it lasts a while does it matter much?