Having had my original thread shredded at St Elsewhere, and my re-loaded version shredded again at the other intermediate place,
![Image](https://i.postimg.cc/zBNsT2rD/FacePalm.jpg)
I have decided to re-document my project a third time which may be of help to others. I will add bits to it over a period of time.
To be honest I think most folk are now going down the modular pylontech battery or other commercial battery as the cost of building your own battery bank is not much cheaper anymore but it may be of use to some folk who like tinkering with stuff.
![Twisted Evil :twisted:](./images/smilies/icon_twisted.gif)
Nowty Towers Batteries
The bulk of my lithium battery bank comprises of re-used Growatt batteries originally used in the Growatt SP2000 system. I bought up generally faulty ones a few years back around 2017. It always turned out the cells were fine, but the control boards were faulty and I managed to buy at an average price of a little over £100 per kWh so they were as cheap as lead acid at that time.
The original Growatt battery unit comprised of 2 x 24v quite handy module racks which were easy to pull out.
The gross capacity of each unit was about 4.8kWh with each 24v module rack being about 2.4 kWh.
![Image](https://i.postimg.cc/fbRh67F6/Growatt-Battery-002.jpg)
Using a bench top power supply and a 1 ohm power resistor, I charged or discharged the module cell packs to manually balance them all up.
![Image](https://i.postimg.cc/jdyTmFKS/Growatt-Battery-003.jpg)
![Image](https://i.postimg.cc/CM6swqp4/Battery-Discharger.jpg)
I first used them in a SMA Sunny Island 24v system and set them up as lead acid batteries. I set all charging voltage's, bulk, absorption and float to the same voltage which matched a SOC of 80%. Also set the charge temperature compensation to 0mv per degree, i.e. disabled that function.
I parallel’d up all the cell packs with fused croc clip links. Even without any active balancing I found that operating them conservatively between 20% and 80% SOC the cells remained within around 100mv of each other over a period of 6 months or so.
![Image](https://i.postimg.cc/G2K524zX/Growatt-Battery-012.jpg)