Why is it a problem to take the house battery below 50%?
In lead-acid and AGM house batteries, service life depends directly on depth of discharge (DoD). A battery kept at the 50% DoD limit typically delivers 500-1000 cycles, while at 80% DoD that number is roughly halved. That is why the practically usable capacity of a 100 Ah lead-acid battery is about 50 Ah, and loads that draw high instantaneous current, such as levelling, must be planned out of that share.
In lead-acid chemistry, every deep discharge leaves sulphation on the plates that is hard to reverse. The common line taken by manufacturers and industry sources is this: 500-1000 cycles at 50% depth of discharge, roughly half of that at 80% depth of discharge. In other words, the energy you gain each time by using the battery deeper eats into total life faster.
Practical consequences:
- Count half of the Ah figure on the label as usable energy, not the whole number.
- While the levelling system moves the electric jacks, it draws a short but high current. If the battery is already half empty, the voltage collapses under this load; the jacks slow down or stall.
- As battery voltage drops, current draw rises, which can make the GRV485 hit its current protection threshold early.
In LiFePO4 batteries the usable capacity ratio is markedly higher than in lead-acid, so a lithium house battery of the same Ah rating works more comfortably in practice. Whichever chemistry you use, keeping the battery fully charged before levelling is the cheapest measure for proper and repeatable operation of the system.
Full coverage of the topic: Guide to automatic RV levelling