Battery bank

In ABYC E-13, the July 2022 text in this PDF, a battery bank is two or more batteries: in series for voltage, or in parallel for capacity. A note in the section on banks says it plainly: mixed chemistries are not suitable for installation in one bank. A lithium house bank beside a lead starter is not one bank under that rule. A sticker that says "new lithium" on the next shelf does not change it.

What it is

A battery bank is a group of batteries for the boat's loads; on cruisers the starter battery for the engine is usually separate. Lithium gives more usable capacity and different rules. It is not automatically better for every boat. Resting voltage does not check one bank. A monitor helps, and a load test and a look at how the bank behaves are still needed.

The same standard requires a switch or another disconnect, independent of the BMS, on each battery or bank, except the system's own output disconnect. It is placed so it can be reached without a tool, as close to the battery as possible. There are no direct connections that bypass the BMS, except those the maker specified. If the BMS suddenly disconnects the bank, starting, propulsion and navigation lights need another source. Before a parallel connection, if the maker set a limit on the voltage difference, that limit has to be met. An unbalanced parallel connection gives a very large current between the banks. The standard calls a manual 1-2-Both switch, and some automatic combiners, possibly unsuitable.

The Victron Orion-Tr Smart charger is built for two batteries: the starter battery and the alternator charge the service battery through a DC-DC converter, without making them one permanent bank. There are models with an isolated ground. Soundings writes about a lithium installation: a Class T fuse on the output, for an interrupt of about 20,000 amps of short-circuit current, on each battery before the bus, cables of one length, and the batteries equalized before they are paralleled. These pages do not give one amp-hour capacity from the length of the boat. Nearby on the site: shore power, bilge pump, diesel heater and survey checklist are other pages, not this amp-hour table.