Overbanking means having a battery bank oversized compared to charging power (particularly in solar-only scenarios). The solar:battery ratio might be something like 1:2. Overbanking is the opposite of overpaneling.
Lithium chemistries are not bothered by partial state of charge so overbanking is a non-issue for them. The camper might have a lot of lithium capacity to take advantage of alternator charging or shore power charging (via converter or stand-alone charger).
Problems can crop up when a 'dweller unintentionally overbanks: “Hi guys! I just bought 400Ah of AGM batteries and a 100w solar setup!”
Unintentionally overbanked designs are also found where a 'dweller wants to run large inverter loads and forgets how much power it takes to recharge the batteries fully every day. Failure to recharge fully leads to battery murder.
Adding alternator charging or shore power charging to solar can help oversized banks stay healthy.