Small AGM holding voltage but not amps.

[loanrangie]

I have a mottobat AGM that i put in my Daytona 7 1/2 years ago that will no longer crank the bike, took it out and put it on a charger overnight just to see if it was in fact toast.
Disconnected the charger and it measured at 13.3V, 2hrs later its still holding 12.9V.I thought maybe it was an earth issue which Triumphs are known for so made up another earth direct to the frame.
Got barely 1 turn out it of so back out and on the bench, still at 12.9V so i hooked up my TJM OX compressor and it happily ran for 5 mins before i stopped it.
Measure again and now at 12.87V ? Obviously the 955CC 3cylinder needs a few more amps to kick it over but i surprised that it still holds a reasonable voltage but the CCA has died, i expected it to be a parallel loss of both ?

[Graeme]

Check the voltage the battery drops to while trying to crank. If it doesn't drop then the problem isn't likely to be the battery.

[loanrangie]

Check the voltage the battery drops to while trying to crank. If it doesn't drop then the problem isn't likely to be the battery.

I guess i could get a kid to hold the mm as starting the bike is a 2 handed affair.

[Slunnie]

If the CCA isnt there I'm betting you're lookin g for a new battery. An auto battery shop can load test the battery and tell you pretty quickly.

I had the same prob, but made more confusing because the 2nd battery died at the same time.

[Homestar]

As others have said - check volts while trying to crank. Could be a US starter on the bike, but it does sound like an odd battery failure.

[Blknight.aus]

not so strange, AGMs have been known to crystalise internally.

if about 1% of the normal surface area of each cell is in touch with tenough of the goopy acid stuff you'll see the right voltage, try to make it do anything though and the volts just go away.

[BradC]

not so strange, AGMs have been known to crystalise internally.

Yep. The plates degrade and either fret away or sulphate up (or both). In all cases you'll still see it hold a "charge", but both the internal resistance and capacity drop away to buggery.

I have a 7.2Ah battery here that will happily run a 5W lamp at what seems like a normal voltage, but it holds about 2Ah of charge and if you put a 21W lamp on it the voltage tanks.
That's pretty much expected as a battery ages.

[loanrangie]

I'm happy with the 7 years I got out of it so was going to replace it anyway, might be OK for a small solar light.

[DiscoMick]

Might be cactus, but have you tried putting it on a multi-stage charger for a week or two and seeing if it can be revived? Might desulphate if you are lucky. Or not.

[loanrangie]

Might be cactus, but have you tried putting it on a multi-stage charger for a week or two and seeing if it can be revived? Might desulphate if you are lucky. Or not.

7 1/2 yo so i wont bother, its not likely have much if any life left - it has been on a multistage previously.