Just to be clear - you say 50% Depth of Discharge is what you're looking at as a kind of rule of thumb. Unfortunately this is a rule of thumb that can you get you seriously burned. You need to look at the figures for the actual battery. Different batteries will have wildly DoD vs. cycle characteristics. The relationship between DoD and cycles is a complex one, that varies per battery.
Some batteries can do 1000s of cycles at minimal DoD (e.g. 20-30%, falling to 100s of cycles when you get to 80% DoD), whereas others can be comfortable doing much deeper cycles without it impacting cycles as much. It depends on the specific build and chemistry of the batteries themselves.
Let's run through a few examples:
I can't find that diagram for Excis FMF 102 -- i.e. the one at Makro mentioned above, but on closer inspection (and thanks to google - here:
http://www.battery.co.za/wp-content/themes/battery/dl/Batteries and Inverters.pdf) the warranty label says:
The battery must:
- be fully charged within 24 hours of discharge (check, should be fine charging by the grid... provided your charger is up to it!)
- not be overcharged (again, need the right charger for it)
- not be over discharged by more than 80% or cycled at more than 50% of its nominal capacity (ok, so 50% DoD seems at the limit, but fine)
This battery carries a limited 12 month pro-rate or 250 cycle warranty.
However failure to comply with these instructions will void the warranty..."
=> so, even if you go to 51% DoD warranty will be void, and moreover, even if you do keep it within the limits, your warranty is only for 250 cycles... so better make sure you don't get load-shedded every day!! Also that warranty is 'pro-rated' so if it does last 11 months, you'll only get 11/12ths of your money back. That sucks if you ask me!!
There are some much better deep cycling batteries that last much longer. For example:
http://www.solarsolved.co.za/datasheets/batteries/sonic/sonicbattery.pdf
This one
Can do just over 1500 (c. 5 years daily cycle) cycles when discharging to 50%... but could do over 2000 (c. 6 years) if discharging to just 40%.
Alternatively there is this one from Raylight:
http://www.solarsolved.co.za/datasheets/batteries/FNB/msolarspecs.pdf
That one would last 2,500 cycles on a 50% discharge -- so flipping long life! (8 years or so!?), in fact it says it would even last 1500 cycles even if it is discharged to 80% DoD. It will even last about 1000 cycles at 100% DoD!
So you see, the rule of thumb of 50% DoD will mean a Dead Excis battery, a 5 year life on Sonic Gel and almost 8 years on a Raylite Solar.
Batteries are not created eqDoes that make sense?
PS - I've got no attachment to solarsolved, they just came up when I googled solar batteries... and they had the spec sheets there online... so thought I'd link to them!
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