In message , Fredxxx
writes
On 18/09/2016 15:46, Tim Lamb wrote:

Worth trying a few charge/discharge cycles. Run the battery down using
the car lights then re-charge. If it won't start the engine after a few
cycles it is junk.

I can't disagree more.

A flat lead acid battery will generally only deteriorate when left
discharged. Charging and recharging won't help. The best state to leave
a battery is in a fully charged state.

https://en.wikipedia.org/wiki/Lead%E...lfation_and_de
sulfation

Sulfation is a one way trip.

I can only speak from experience. More years ago than I care to
remember, I was working at a Vickers Shipbuilding model tank. For open
water trials models were powered by a stack of lead acid batteries.

The battery room had shelves of batteries around 45 amp/hr. capacity and
mostly flat as your hat. My boss was of the same opinion as you *once
flat = scrap*. The budget for the trial was pretty much petty cash as it
was for a timber stern trawler being made at Berwick upon Tweed and
certainly not MOD.

After a few charge/discharge cycles the batteries worked well enough for
the performance trials at the Dumbarton test tank and open water
demonstration at Berwick.

Trying won't cost anything other than time.

--
Tim Lamb