Charging the marine battery for the boat, the charger lets you select 10/20/40?

Question

what should you select to get a full charge

Answer 1

just charge the d**n thing!

Answer 2

Joe has got the answer, well said.

Answer 3

What's the best way to charge deep cycle batteries? The maximum charger rate in amps should be 20% of the amp hour rating of the battery.

Normally, deep cycle batteries do not require special charging procedures. However, we recommended that you use a charger designed specifically for deep cycle batteries. It is best to slow charge all batteries, especially deep cycle. The 20% rule should be used when charging a deep cycle battery. That means to choose a charger where the maximum current (in amps) is less than 20% of the Ah rating. For example, an Interstate SRM-27 is rated at approximately 100 Ah, so a 20-amp charger should be the maximum. Also, it is best to use a charger that is adequate to recharge the battery within 10-12 hours (see next question).  

TOP How long should I charge my battery and at what current? Generally, we recommend that you use a low amp charge, i.e. as low as the battery will accept, over a longer period of time. A 10-20 amp charger can charge most automotive batteries. Fully charging a completely discharged automotive battery, for example, with a 10-amp charger may take approximately 6-10 hours at a temperature of 80°F. Lower ambient temperatures require a longer charge time.

Some chargers automatically adjust the current and length of charge according to the battery's state of charge and then shut off when the battery is fully charged. If the charger requires manual adjustment for current or shut-off, check the charger's instructions to determine the proper current and length of charge based on your battery's rating.  

TOP What will happen if I don't charge my battery properly? The two extremes of improper battery charging are under charging and over charging.

Under charging results from a failure to allow the charger to charge long enough to restore the battery to full state of charge. Continually operating the battery in a partial state of charge or storing the battery in a discharged state will result in a condition known as sulfation. Sulfation reduces the battery's performance and may cause premature battery failure.

Over charging causes accelerated corrosion of the positive plates, excessive water consumption, and in some cases, damaging temperatures within a lead acid battery. Deep cycle batteries should be charged after each discharge and/or after storage of 30 days or more. We recommend that a deep cycle battery not be discharged below a 50% state of charge. Recharging a severely discharged battery (below 50% state of charge) can result in the battery becoming overheated or overcharged.

Answer 4

If you don't want to read Joe's excellent answer, just put it on 10 and leave it alone until it is charged.

Answer 5

for a thorough charge put it on the lowest charge rate and leave it on that until the battery is charged.