Modern fishing boats have multiple batteries. After a long day of fishing, the batteries will be low on energy. To recharge takes time. You may be planning to recharge the batteries so you can fish the next day. Try Charging two batteries at the same time.
Connect your batteries in parallel. This means + to + and -to -. Use 10-gauge wire with round connectors. Make sure that the terminals are clean. This will improve the contacts needed for more efficient charging. Use an automatic Trickle Charger that can regulate the charge as the batteries get nearer to being full. Charging too long wears out the plates and adds corrosion that will shorten the batteries life. ￼
RV’s may have a built-in system to keep batteries charged and ready. Modern plastic fittings have a tendency of cracking and failing, especially during severe cold conditions.
Multiple batteries take longer to charge but you will not need to get up in the middle of the night to switch the charger. You also need at least a 20-amp charger to account for the extra load. It will take twice as long to charge 2 similar batteries. It does not matter if the 2 batteries have a different amount/need of charge. If the 2 batteries are far apart on charge level, the lower charge will take need time. The higher charge battery will fully charge first. If time is important, charging the lower charged battery separately may be smarter. ￼
Use a voltmeter to check the charge.
12.6 V is 100% charged
12.4 is 75% charged
12.2 is 50% charged
12.0 is 25% charged
11.9 is discharged
Storing batteries properly is important. Modern batteries can be stored on cement floors. Charge the batteries fully and store them in a cool place. An automatic trickle charger is a good idea to keep the battery from falling below 12.4 Volts. Keep the battery disconnected from the boat or accessory. Keep the batteries stored safely in a cool, but not freezing area. Subzero temperatures will freeze a discharged battery. I remove them from the vehicle and keep them in the garage.
Handle batteries carefully to avoid spilling any corrosive chemicals. If you spill the chemicals/ liquid/ gel, you will need to cover the spill with Baking Soda. Then add some water and mix into a slurry. Now you can clean up the mess. Wear eye protection and rubber gloves to avoid any contact.
Now it’s time to start up!