Lithium vs. AGM, without the fake scorecard

Every battery on the old Megawatt calculator is a Vatrer lithium pack. So this isn’t a neutral shootout. It’s what the calculator assumes, and what you should check yourself before you swap chemistries.

How the watt-hours are counted

The calculator treats a 12-volt 100Ah pack as 1,280 Wh and a 300Ah pack as 3,840 Wh. That’s 12.8 volts times amp-hours, the usual nominal voltage for LiFePO4 (lithium iron phosphate). It’s a planning figure, not a test Megawatt ran.

Where AGM fits

AGM is a sealed lead-acid battery. Owners plan on using only part of its rated amp-hours, because deep discharges shorten its life. The battery runtime calculator lets you set that usable fraction yourself. It doesn’t guess one for you.

Get the rest from the spec sheet

Cycle life, weight, and cold-weather charging limits all vary by model. Pull them from the maker’s spec sheet for the exact battery you’re looking at, not from a comparison chart.

When the voltage changes

The calculator picks system voltage from your continuous watts. Up to 3,000 W it stays at 12 volts. From there to 5,000 W it moves to 24 volts, and above that, 48. Those cutoffs come from James’s original widget, not from an electrical code.

A higher-voltage bank means a different charger and a different inverter. For most owners, that’s the point where a pro does the install.

Before you swap

Match the pack to the calculator’s net storage number. Then read the battery maker’s manual for charging voltages. Fleetwood’s house electrical chapter says the coach electronics are voltage sensitive, and a stock converter may not charge lithium the way the maker wants. Check its charge profile before the new bank goes in.