March 20, 2026 The My Mestic Team

Second-Hand Leisure Battery: How to Test Before Buying

Second-Hand Leisure Battery: How to Test Before Buying is one of the most searched topics among campervan and caravan owners, and with good reason. Getting your battery setup right underpins everything else in your 12V system. This guide gives you clear, actionable steps based on real-world practice.

Before You Start

Understanding your current setup is the first step. Check whether you have a lead acid, AGM, or lithium (LiFePO4) battery, as the procedures differ. The Mestic MLB-100 Smart (100Ah lithium with built-in BMS and app control) and MLB-300 Smart (300Ah) are LiFePO4 chemistry, which has specific charging requirements that differ from older battery types.

Gather the right tools and materials before you begin. For most battery work you will need a multimeter, appropriately rated cables and fuses, cable crimps or terminals, and basic hand tools. Never work on battery systems with rings or metal watches on, and always disconnect the negative terminal first when removing a battery.

The Process Explained

Start with a clear plan of what you want to achieve. Draw a simple wiring diagram showing your battery, fuse box, charge sources (solar, alternator, hook-up charger), and loads. This prevents mistakes and makes future troubleshooting much easier. Label every cable at both ends.

For a standard leisure battery installation, the sequence is: mount the battery securely, connect the negative cable to a common ground point, install an isolation switch on the positive cable, connect the positive through an appropriate fuse to your distribution panel. The Mestic MLB-100 Smart at 100Ah provides a solid foundation for most campervan builds, with app monitoring so you can track state of charge from your phone.

Testing and Verification

After completing any battery work, test before buttoning everything up. Use a multimeter to check voltage at the battery terminals and at each connection point. A fully charged LiFePO4 battery reads approximately 13.4V, while a fully charged AGM reads around 12.8V. Any significant voltage drop between the battery and a connection point indicates a poor crimp, loose terminal, or undersized cable.

If you have installed the Mestic MLB-100 Smart or MLB-300 Smart, open the Mestic App and verify that cell voltages are balanced and the BMS is reporting normal status. This gives you a known-good baseline to compare against in the future.