By Boat Battery editorial team · 2 minute read · Editorial policy
Ask for the installation history, equipment identities, diagram, settings and supporting records. A tidy battery case and a full-charge display do not establish the condition of the system.
Inventory batteries and charging equipment
Make an equipment inventory before discussing claimed value. Identify the exact battery models, installation dates, charging sources and monitoring equipment. Compare the labels with invoices and warranty records where available. A description such as ‘new lithium system’ can hide a mixture of new batteries and much older charging hardware.
Check installation history and retained wiring
Ask who designed and installed the conversion and what was retained. Request the final diagram and any applicable commissioning or compliance documents. Look for records of later changes: an added inverter or additional battery may alter the loads and protection assumptions of the original installation. Missing paperwork does not prove a fault, but it creates a question that needs resolving.
Define the pre-purchase inspection
Include the battery system in the scope of an appropriate pre-purchase inspection. State of charge is not state of health, and a short viewing is not a capacity test. Agree any testing with the seller and qualified inspector, including safe procedures and what the result can establish. Do not accept a single app screenshot as evidence of remaining service life.
Confirm warranty and owner handover
Finally, check the practical handover. Confirm access to monitoring devices, transferable warranty terms where relevant and how the system should be operated or laid up. Budget for documentation gaps or necessary corrections before comparing boats. A well-documented installation is easier to maintain, but records should still be checked against what is physically aboard.
Request with the vessel documents
- Battery and charger models, dates and serial numbers
- Installer invoice and final wiring diagram
- Settings and commissioning records
- History of changes, alarms and repairs
- Inspection scope and warranty-transfer conditions
Frequently asked questions
Does a 100% display mean the battery is healthy?
No. It is an estimate of present charge, not a measurement of remaining capacity, service life or installation quality.
Related installation planning resources
Use these notes to prepare your own measurements and questions. Check the exact equipment manuals and have the proposed system assessed for your vessel before buying or changing electrical components.
Calculate your boat battery capacity
The house bank calculator takes your loads, your nights on the hook, your solar and your alternator, and returns the bank, the DC-DC charger, the AGM equivalent and the weight you take off the boat.
Open the calculator