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.