I have four, 6v batteries (L16 I think) that, although they have never been used, have been sitting for nearly 7 years without any charging or maintenance. Is there any hope for them?
First answer... Sell them to a battery recycler for the lead.
Second answer... There are people/processes out there that "claim" to recover dead batteries. Flushing out the old acid, various recharging methods, replacing the acid/electrolyte. And even one that turns them into "alkaline" batteries.
The second answer is messy, possibly hazardous (and hazardous wastes). And is nothing I would suggest that anyone do, ever, if they want to use them in a normal battery bank with lots of current and energy storage with long life.
Probably not if they were stored near or above room temp.
I'd check them over for any physical damage (eg freeze induced cracking/bulging, dried up electrolyte), and if they seem okay I'd try charging (carefully). Ya never know.
There is no physical damage and the electrolyte level is at least reasonable. As they are brand new (although ageda bit I may just connect two together and apply 10 amp automotive charger (all I have available) and see what happens...
I am curious as to what actions take place over time in this state that cause deterioration.
As they discharge the acid weakens as Sulphur is deposited onto the plates, which will harden to the point it cannot be returned into the sulphuric acid electrolyte. After a year of sitting they are usually beyond recovery, 7 years, don't waste your time.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.
uuugh. oh well.
Thanks for the explaination, i wonder what value have they have at the recycler... (if any)
Shop around. It may also depend on your state laws on recycling/core charge recovery fees/etc.
Lead acid batteries are among the most recycled products on the planet.
In my area, they have a refundable per-core charge (currently ~$30ea). In some area, I think it's a variable per-pound amount. Like Bill says, maybe shop around.
I agree with LH2 that they're likely goners. Attempting to charge would be mostly just for the heck of it. I'd probably have a go, but I'm just like that.