LiFePO4 Batteries

Cycle life and usable depth. Discharging lead-acid past 50% shortens its life sharply, so a 100 Ah lead-acid battery realistically gives you 50 Ah; a 100 Ah LiFePO4 gives you 80–100 Ah and does it for five to ten times as many cycles. Over a decade LiFePO4 is usually cheaper per usable kilowatt-hour despite the higher sticker price.

Not without damaging it. Charging LiFePO4 below 0 °C causes lithium plating and permanent capacity loss. Discharging in the cold is fine. If the battery will live somewhere that freezes, buy a model with a built-in low-temperature cutoff or self-heating — many now include it, and the spec sheet says so.

A battery management system protects the cells from over-charge, over-discharge, over-current and temperature extremes, and keeps the cells balanced. Every reputable drop-in LiFePO4 battery has one built in. If a listing does not mention its BMS, treat that as a reason to look elsewhere.

No. They have different charging voltages and curves, and paired together the lithium will take most of the load while the lead-acid stays chronically undercharged, damaging both. Replace the whole bank at once, and reconfigure the charger to a lithium profile while you are at it.

Work out your daily consumption in watt-hours, then divide by the system voltage to get amp-hours. Add headroom for cloudy stretches — two to three days of autonomy is the usual off-grid rule. Note that amp-hour ratings are quoted at a specific voltage, so a 12 V 100 Ah battery is 1,280 Wh, not directly comparable to a 24 V 100 Ah one.