I just want to share my DIY upgrade, perhaps someone will consider it useful.
After disassembling original pack - there are 5x Sony VTC4 US18650VTC4 batteries inside ( 2100mAh max 30A ).
Initially the plan was to open battery box and solder extra cells directly to original pack, but then I decided to extend wires and make it external.
This will allow to add more cells if needed.
I didn't had exactly the same cells so I added similar Samsung cells with higher capacity and lower max current (2500mAh 20A).
Current isn't a problem as I have now 2x cells in parallel, to balance them properly I had to connect 5 balancing wires.
14AWG high quality wires for power output and thinner 20AWG wire for balancing (sorry I only had one color - red ).
Total capacity ~5.5Ah.
I was planning to add GPS inside the mower, but I though adding them into battery will let it work ever with battery disconnected.
Added power connector for GPS module to switch it off during winter.
Total cost ~30EUR:
- 5x Samsung INR1865025R - 2500mAh, 20A ( 5x3.4EUR= 17EUR)
- cheap GPS tracker from china - 10EUR
- some wires and plastic cells holders - 2-3EUR
Works perfectly so far - much longer mowing time, less charging cycles. Just need to put everything into nice looking heat wrap.
Very happy about this upgrade.