12v 17aH SLA battery is at 9v - is it dead?

[Fallingwater]

I agree partially.
The sulfation-sulphation is really a non-problem, so spell it as you want and I won't be a grammar nazi anymore but I cannot stand ppl who writ lik dis on the net.
I can understand shortening in SMS messages, where you pay every 160 characters and have a ten-key keyboard, but there's no excuse for writing that way when you have a 101-key keyboard and loads of bandwidth.

Rant concludes, let's go back on topic.

 

[MrAl]

Hi,

Back on topic (ha ha)...

You can easily test your battery to see if it's bad.
Run a test current into the battery as if you were going to charge it up.
If you ran it down to 9v then when you connect the charge current the
voltage jumps up to 14v in about 10 seconds you know it's dead.
It normally takes 17 hours at 1 amp (plus ineff's which i wont bother you with)
to charge it up, so if it charges in 10 seconds (or even a few minutes)
you know it cant be taking a charge properly.
If it takes one hour than your battery has roughly 1 amp hour capacity left.
Of course this is a *very* rough estimate, as it's really about 1/3 less than
the charge that goes in, so for 1 hour charge you get out 40 ampere minutes,
or for 1.5 hours charge (still at 1 amp) you get out 1 ampere hour. You can
roughly guess the remaining capacity retention by doing the charge and then the
calculation. Of course if your battery comes out looking like it can hold
about 8 ampere hours then it lost about 1/2 of it's original total capacity
if it's a 17 ampere hour battery.