It is possible for a leisure battery to drain the main battery, but it would depend on how the leisure battery is connected and used.
If the leisure battery is connected directly to the main battery and both batteries are used simultaneously, there is a risk that the leisure battery could drain the main battery if it is not properly managed. This could happen if the user is not monitoring the charge level of the batteries, or if the leisure battery is drawing more power than it is being replenished.
However, if the leisure battery is connected to a separate charging system, such as a solar panel or a battery charger, and is only used when the main battery is not in use, then there should be no risk of the leisure battery draining the main battery.
Overall, it is important to properly manage and monitor the charge levels of both batteries to prevent any issues.
Let me explain in more detail.
A leisure battery is typically used to power appliances and devices in a recreational vehicle or boat when it is not connected to an external power source. In contrast, the main battery in a vehicle is used to start the engine and power the vehicle's electrical systems while it is running.
If a leisure battery is connected directly to the main battery, for example, using a split charging system, it is possible for the leisure battery to drain the main battery if it is not managed properly. This can occur if the leisure battery is used at the same time as the main battery, or if the leisure battery is not being charged properly.
For example, if the leisure battery is being used to power appliances in the vehicle while the engine is off, it will draw power from the main battery. If the user does not monitor the charge level of the batteries or if the leisure battery is not recharged properly, the leisure battery may eventually drain the main battery. This can lead to the main battery not having enough charge to start the engine.
On the other hand, if the leisure battery is connected to a separate charging system and is only used when the main battery is not in use, such as when the engine is turned off, there is no risk of the leisure battery draining the main battery. In this case, the leisure battery is charged separately from the main battery, ensuring that each battery has enough power for its intended use.
To summarize, while it is possible for a leisure battery to drain the main battery, it can be prevented by properly managing the charge levels of both batteries and ensuring that the leisure battery is connected to a separate charging system.