AGM battery dead-revived

[Sp0_0k]

Just wanted to share some of my experiments and tests.
Leisure battery dies after 5 years, just because cali left in the garage without hookup and small load left inside.
Voltage 3v. First thought of throwing it away but decided to play with it a bit.
-First surprise, the hookup charger doesn't refuse to charge but loads 14v at ~13amps.
-Voltage starts to drop to 13 and amps rising (probably internal resistance dropping)
-Battery accepted over 75 AH to 14,4v level, which left me totally puzzled. The battery was slightly warm so no idea where all that energy went.
-Now important part how much will it give back. Battery delivers 35 AH back at ~10amps load, cutting at 11,6v ( Was around 35-45AH before dead discharge)

Conclusions. Dead AGM is recoverable and even with hook up cali charger.
I don't see a very significant capacity drop just a slightly higher voltage sagging under load (down to 12,2V at full charge and 10 amps load)
So don't panic and don't hurry to throw the battery away.
P.S. what puzzled me more, that the main car battery (exactly the same 75AH AGM) had around effective 25AH left in it, and it was never deeply discharged.
Somehow it wore out way more, with way smaller and more frequent cycles and of course burst discharges for starts.

 

[Sp0_0k]

As a note, the only and reliable battery test is testing its full effective capacity, internal resistance and voltage drop under the load (which directly measures the internal resistance)
You don't need any fancy charges for it but a simple hobby DC-DC charger that lets you see the current flow. Those chargers also have a very nice feature of discharging into the other battery load, allowing high amps discharge tests.
So you put 2 batteries together and flow the charge back and force testing