Thread: Starter + leisure battery

Hi popotla, even with the two batteries connected in parallel, because of a number of factors, the cranking battery will still provide most of the current while starting the battery.

The difference in the physical structure of the two batteries means the bulk of the current will still be coming from the cranking battery.

The size and length of the cabling connecting the auxiliary ( leisure ) battery will also reduce the current draw coming from the auxiliary battery.

The end result is that you will not harm a deep cycle type auxiliary battery but by reducing the current load on the cranking battery, even by a small amount, you will improve the life span of the cranking battery, and this is also because of a number of factors.

First off, as above, you are reducing the total amount of energy the cranking battery has to provide during cranking.

This then means you have less used energy to replace, and that then means it will take a shorter drive time to recharge BOTH batteries.

Your setup is actually a win, win situation.

However doesn't the situation change somewhat if the deep cycle battery (leisure) is significantly discharged, the cranking battery will be supplying a bulk charge to the leisure and attempting to crank the engine at the same time?

Originally Posted by Lotz-A-Landies

However doesn't the situation change somewhat if the deep cycle battery (leisure) is significantly discharged, the cranking battery will be supplying a bulk charge to the leisure and attempting to crank the engine at the same time?

Very true, but this would only apply when the batteries have been separated and the auxiliary battery has be discharged while camping. It is still a good situation to cover.

In this case, the ideal ( and safest ) operation would be to start the motor first, then link the batteries.

At all other time, when there is no accessories running off the auxiliary battery, just leave the batteries connected together