Every AmpereArc pack uses lithium iron phosphate cells. The reason is not marketing preference; it is two measurable properties.
Thermal behaviour. LiFePO4 has a markedly higher thermal runaway onset temperature than the nickel-manganese-cobalt chemistry used in most consumer electronics, and it does not release oxygen as it decomposes. That is a genuine difference in failure mode, not a claim that the chemistry cannot fail.
Cycle count. 6,000 cycles on the 5 kWh residential pack, and 4,000 – 6,000 on the 16 kWh. At roughly one cycle a day, that is over a decade of daily use before capacity fade is the conversation.
Neither of those makes it the right chemistry for every job — it is heavier per kWh than the alternatives, which is why it is not what is in your phone. For a fixed installation that has to sit in a plant room for fifteen years, the trade is the right way round.
Temperature
Both residential packs are specified for 0 to +55 °C charging and −20 to +55 °C discharging, with natural cooling and indoor mounting.
The one that catches people out is the charging floor. Below 0 °C the BMS will refuse to charge, and correctly so — charging a lithium cell below freezing plates lithium metal onto the anode and permanently costs you capacity. An unheated garage in January is a real risk; an internal plant room is not.
At the other end, a pack in a sealed cupboard with no airflow will derate rather than fail, but it will spend its life doing so. Both packs cool by natural convection, which means they need air around them, not a fan.
Depth of discharge
The packs are set to 90 % depth of discharge, which is where the "5.12 kWh rated, 4.5 kWh usable" gap comes from.
You can be more conservative. Setting the inverter to hold a higher reserve costs you usable capacity every day and buys you cycles at the far end of the pack's life. For most households that is the wrong trade — the capacity is worth more now than the cycles are in year twelve. It is worth revisiting if the system is oversized for the load, which is a good problem to have.
The twice-yearly check
Twenty minutes, no tools beyond a torch:
- Look at the terminals. Any discolouration, any greening, any sign of heat. Loose terminations get warm before they get dangerous.
- Look at the ventilation. Nothing stacked against the pack, nothing stored on top of it, air path clear.
- Read the state of health in the app rather than guessing from behaviour. A slow drift is normal; a step change is not.
- Check the BMS communication cable. The RJ45 between pack and inverter is the single most common loose connection in the whole system. Push it until it clicks.
What not to do
Do not open the casing. There is nothing user-serviceable inside, the DC bus is live at 51.2 V nominal, and opening it ends the warranty.
If a pack is behaving oddly — refusing to charge, tripping, reporting a cell imbalance — leave it in the state it is in, isolate it if you can do so safely from outside the enclosure, and call us. A photograph of the display and of the pack's own status lights answers most of these without a visit.