[AusNOG] EOL Battery Strings

[Ross Wheeler]

Cripes, you guys are all weirdos!
I didn't expect to get innundated with requests... forgive me please 
moderators, for this semi-off-topic post. All those who emailed me 
directly, I'll try to get back to you and your individual questions and 
requests as soon as I can.

For those who didn't ask already, or who have - perhaps this will address 
most of the more common questions!

Cells seem to be removed from service after a given time, regardless of 
how many cycles they have (or have not) done.

Cells typically lose capacity due to internal sulfation buildup on the 
plates and/or loss of electrolyte. Sealed cells can still dry out, 
especially if they are floated at too high a voltage.

When buying ex-data-centre cells, it's a gamble what you'll get.
Recovering AGM cells is an inexact science and no guarantees you'll get 
any good cells out the end of it. They are however generally pretty cheap.

For anyone wanting to go "off-grid" for their home, I'd strongly suggest 
doing a REAL cost-benefits analysis for your specific site. It is almost 
certainly cheaper to use the grid. If you MUST or REALLY WANT TO go it 
yourself, you'll almost certainly underestimate the capacity you will 
need. AGMs are sensitive, finniky things that are easily destroyed with 
over-charging, over-discharging or simply cycling too deeply. Flooded 
lead-acid cells (traction batteries, forklift packs etc) are far more 
forgiving of abuse.

I've lived 100% offgrid for almost 10 years now, and been through a few 
cells. Because my home and office is underground, venting FLA cells is 
problematic. To get decent cell life, plan on a MAXIMUM discharge of 20% 
of the batteries claimed capacity. (Eg, 2V/500AH cells, plan to discharge 
them no more than 100AH. In a 48V bank, that's under 5kWh usable capacity 
between sundown and sunup (best case, clear weather, solar panels on 
tracking frames, etc... for most of you, that 5kWh will be from 
mid-afternoon to mid-morning, and that's a BIG ask!)

I've recently replaced 2 banks (48V/1000AH) of AGM with 300AH or LiFePO4 
which are about 1/8th the space and 1/10th the weight of the AGMs they 
replace, with slightly more usable daily watt-hours capacity).

Batteries are NOT a "buy, connect, forget" investment. You will need to be 
dedicated and committed to them to get a decent life from them. You will 
need to adapt how you use power. But if you can/do, the benefits of being 
self-sufficient are substantial. (I've had zero power-failures in the 
almost 10 years I've been here... it was rare to go a few months without a 
power fail while I lived in town on-grid).

Again, sorry for the off-topic post, and I'll try to get to all the 
private emails soon.

RossW